Ron Ananian, The Car Doctor - July 11, 2026 Hour 1 - The Double Whammy Jeep Air Conditioning
Ron Ananian The Car Doctor
Ron Ananian, The Car Doctor - July 11, 2026 Hour 1 - The Double Whammy Jeep Air ConditioningRon Ananian The Car Doctor · Jul 11, 2026
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Term
air conditioning problem
“AC problem” can mean a lot of different things, like low refrigerant, a bad sensor, or an electrical/control issue. The mechanic is saying you can’t assume the cause just because the air isn’t cold.
The Jeep Grand Cherokee is a popular Jeep SUV. In this part of the episode, the mechanic is working on a 2015 model’s air-conditioning problem, and he explains why diagnosing AC can be tricky on older, higher-mileage vehicles.
The “check engine” light is a warning on the dashboard that something in the car’s systems needs attention. The mechanic checks it first because it can point to a code that helps figure out what’s wrong—sometimes even when the issue seems like it’s just the AC.
Fault codes are numbers the car stores when it detects a problem. A scan tool reads them, and that helps the mechanic figure out where to look instead of guessing.
A catalytic converter fault code points to a problem in the exhaust emissions system. The mechanic is mentioning it because sometimes the car shows codes that aren’t directly about the AC, which can throw off the troubleshooting path.
P0430 is a specific “problem code” the car can store. It usually relates to how well the catalytic converter is working, and in this story it’s mentioned because it may be unrelated to the AC symptom.
Term
evaporative
“Evaporative” refers to the system that controls fuel vapors from the gas tank. The mechanic is hinting that there may be codes related to that system too, not just the AC.
This code is about how fast the engine warms up. If the engine doesn’t heat up quickly enough, the car may think something’s wrong and may change how other systems behave, including shutting A/C off.
When the car detects a problem, it can save a “snapshot” of what was happening right then. That snapshot is called freeze frame and it helps the mechanic see the conditions that triggered the warning code.
A/C operation means the car actually turns on cooling. Sometimes the car’s computer won’t allow A/C to run if it detects a related fault, even if the A/C parts themselves aren’t obviously broken.
An A/C machine is the shop tool that connects to the car’s A/C to pull out old refrigerant and put the correct amount back in. It also helps the mechanic measure what the system is doing.
Refrigerant is the fluid that makes car A/C cool. If the system loses refrigerant, the A/C won’t work well, and the mechanic has to figure out whether it’s leaking or just slowly disappearing over time.
A vacuum pump pulls air out of the A/C lines. If the pressure stays steady for a long time, it usually means the system isn’t leaking much (or at all).
Refrigerant charge is how much cooling fluid is in the A/C system. If it’s low, the A/C may not cool correctly and the system may not run the compressor properly.
Term
CO two
He’s talking about using CO2 to help find where the A/C system is leaking. It’s a way to test the system without immediately adding costly refrigerant.
That “twelve thirty four yf” is the name of a specific refrigerant used for car air conditioning. He’s saying it costs a lot, so he wants a cheaper way to test for the leak first.
The compressor is the part that actually makes the A/C system work by moving the refrigerant. If it won’t turn on, the system can’t cool, and there’s likely a sensor or control problem.
The AC condenser is a radiator-like part for your air conditioner. It helps get rid of heat from the refrigerant. If it gets damaged by road rocks or debris, the AC may not cool well or may stop working.
EVAP is the system that keeps fuel vapors from escaping into the air. A fault means the car’s computer detected something wrong in that system. It can show up as a code even if your AC issue is caused by something else.
A key-on engine-off monitor is a self-check the car runs when the ignition is on but the engine isn’t running. The computer uses it to test emissions systems like EVAP. That’s why a problem can be detected and logged even when the car is parked.
A scan tool is a device a mechanic plugs in to talk to the car’s computer. It can show trouble codes and what the car is commanding in real time. It helps pinpoint whether the problem is electrical/command-related or mechanical.
The engine controller is the car’s main computer for controlling the engine and related systems. It also helps coordinate whether the AC should run. If the ECU gets the AC request but nothing happens, the issue is probably not just the button or wiring.
The body computer is one of the car’s main computers that handles things like switches and interior functions. In this case, it’s involved in sending the “AC request” signal. If it doesn’t send that signal, the AC won’t turn on.
An AC request is the computer’s “turn the air conditioning on” command. The host checks that the car actually registers the button press as a request. If the request is correct but the AC still won’t run, the problem is likely in the parts that physically make the AC work.
A functional test is when the scan tool tries to force a system to run to see if it responds. Here, it’s used to try to turn the AC compressor on directly. If it still doesn’t run, that points to a problem beyond just the normal button request.
It’s the car’s main electrical box that sends power to different systems. If the A/C isn’t working, the problem can sometimes be traced by looking at how the wiring is routed through this box.
They’re using an old headlight from a Chevrolet Chevelle as a simple electrical test tool. It’s basically a known light bulb load to help check the A/C compressor circuit.
It’s a test trick where you temporarily use a different electrical “load” to stand in for a part. That helps you see whether the wiring/control side is working before condemning the component.
EVAP diagnosis means checking the system that keeps fuel vapors from escaping into the air. If there’s a leak or a sensor problem, it can cause warning lights and needs troubleshooting.
In this context, an estimate is an informed prediction of repair cost based on diagnosis, not a guaranteed final price. The host emphasizes that AC work often requires educated guessing because the full scope may only be confirmed after parts are replaced or the system is tested.
Recharging the AC means putting refrigerant back into the system after a repair. If there’s still a leak, the refrigerant will just leak out again, so the fix has to come first.
Term
YF machine
A “YF machine” is the specialized tool shops use to work with AC refrigerant. If the shop doesn’t have the right one, they may have to wait or send the car back later.
This is a 2016 Kia Soul, a small car with a 2.0-liter engine. The point here is that the owner is troubleshooting why the check-engine light keeps coming on.
Direct injection means the fuel is sprayed right into the engine’s cylinders. That can help the engine run efficiently, but it also means small problems can trigger warning lights.
Term
check engine like it popped on
The “check engine” light is the car’s way of saying it found a problem. Usually you scan codes to figure out what system is acting up.
Term
P zero four to four zero
P0440 is a diagnostic code from the car’s computer. It usually points to a problem in the EVAP system, which helps capture fuel vapors instead of venting them to the air.
An EVAP canister (often just called the “charcoal canister”) stores fuel vapors from the tank so they can be burned later by the engine. When the EVAP system can’t hold or route those vapors correctly, codes like P0440 can appear.
Term
TVC valve
A TVC valve is a small valve that controls flow in the car. Here, the mechanic is checking whether it leaks and then replacing it if it doesn’t seal properly.
This is a simple leak test: you try to pull air through and then push air back through the part to see if it seals. If it leaks when it shouldn’t, the part may be bad.
Term
Exxon fuel standard octane regular gas
Octane is how resistant the fuel is to knocking in the engine. The host is saying they used the normal regular gas so the problem likely wasn’t caused by using the wrong fuel.
P0442 is a diagnostic code that usually means the EVAP system has a small leak. Even if you replaced one part, the car may still detect a leak somewhere else in the system.
Gasoline doesn’t just sit there as liquid—it evaporates. Fuel vapor pressure is a measure of how readily it turns into vapor, and that matters because the car has to manage those vapors to meet emissions rules.
The EVAP system is the car’s way of stopping gasoline fumes from escaping into the air. It stores the fumes and later sends them back into the engine to be burned.
The intake manifold is the engine’s distribution channel for air going to the cylinders. The EVAP system can route stored fuel vapors into it so the engine burns them instead of releasing them.
The Clean Air Act is a U.S. law that limits pollution. The point here is that cars have to control gasoline fumes rather than just venting them into the air.
The purge valve is a switch in the EVAP system that opens to let stored fuel vapors get sucked into the engine. That way the vapors don’t just sit in the charcoal canister.
In EVAP terms, “oversaturated” means the charcoal canister has trapped more fuel vapor than it can effectively store. If it gets too full, the system can’t manage emissions properly, which is why the purge/vent strategy matters.
EVAP is the system that keeps fuel vapors from venting to the air. It stores those vapors and then routes them into the engine at the right time, and the car monitors it with sensors.
Purge flow is the amount of fuel vapor the EVAP system is pulling from the canister into the engine when the purge valve opens. The computer infers purge flow from sensor data; if it sees “purge flow” effects without commanding the purge valve, it may flag an EVAP malfunction.
Term
FTP sensor
An FTP sensor is a sensor that sends the engine computer information about fuel/air conditions. If it’s faulty—like if its wiring is shorted—it can confuse the computer and make it think there’s a problem when there may be.
A ground wire is the electrical “return” that completes a circuit. If it shorts to metal, it can make the purge valve act incorrectly even when it shouldn’t.
“Swapping parts” means replacing parts without really proving they’re the cause. The host is saying that can lead to wasted effort if the real problem is something like a wiring or sensor issue.
Diagnostic trouble codes are the computer’s way of saying, “I noticed something wrong.” But a code doesn’t always tell you exactly what part is bad—so you have to figure out what’s really causing it.
Suspension is what helps the wheels stay in contact with the road and smooths out bumps. If nothing in the suspension is loose, it usually means the rattle isn’t coming from a part that’s hanging or broken.
Term
diagnostic purposes
“Diagnostic purposes” refers to using a controlled situation to help pinpoint where a noise or vibration originates. In this case, the speaker uses a driveway approach and listens at specific wheel contact points to narrow down the corner (front vs rear, left vs right).
Heat shields are metal covers that keep hot parts from overheating or damaging nearby stuff. If one is loose, it can rattle and make noise, especially when you hit bumps.
When a car is on a lift, the suspension can hang differently than it does on the road. That can make some noises disappear, so the mechanic may need a different test setup.
That light is the car’s warning that the front passenger airbag isn’t going to deploy. If it stays on, the airbag system likely has a fault and should be checked with the car’s diagnostic scanner.
Term
scanned this for codes
“Scanning for codes” means plugging in a diagnostic computer to read what the car stored as the problem. For an airbag warning, those codes help find the exact cause instead of guessing.
A complete system scan is when the mechanic checks more than one part of the car’s computer system. It helps find hidden problems that might not show up right away.
The airbag light is the dashboard warning that the airbag system has a fault. If it’s on, the airbag may not deploy during a crash, which reduces occupant protection.
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Ronananians. Before I plug in a vehicle, before I open
the hood, before I even write the repair, I want to listen. I want you to sit down and talk
to me. I want to hear what you have to say.
So won't you this new up the manasa? He said
the Car Doctor.
I used the truck to pull a bunch of logs that I cut up on.
My fawmill to make my business.
On the side of the river over here, and dubn truck means so much to me. And I'm going to
be retiring soon and pulling a ten thousand pounds trailerble houseboat.
That's the vehicle to do it with. Let me tell you.
Welcome to the radio home of Ron Andanian, the Car Doctor.
Since nineteen ninety one.
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Up the phone and call in. The garage door is
car open, but I am here to take your calls at eight five five five six ninety nine hundred and now pee.
Running.
I want to talk to you about, well, the perfect storm of thegnosing an air conditioning problem, because this is the one I always dread, and it's out there and it happens every once in a while, and it's a freak occurrence, but it happens, and it's real worlds and it happened to me this week, and I this is why I hate doing estimates. This is why when somebody says, hey,
Ron what's this gonna cost? I don't know. I can
give you a ballpark, but it goes out the window as soon as I touch the car, because anything is possible.
Another repair shop brought us a twenty fifteen Jeep Grand Cherokee that the ACE didn't work. So I know zero
about this car other than that it's a twenty fifteen Jeep Grand Cherokee one hundred and thirty eight thousand miles silver.
Driver's door is kind of tight to open, which I'm seeing a lot of. I'm not sure if anybody's got
a Jeep of that generation, I'd be curious what they're experiencing because as these get older, that driver's door hinge seems to bind or rust or stick something. There's something
weird going on there. This is the fourth one I've
seen in the last two years, so it's not it's not you know, the one. The first one I saw.
The car was in an accident and supposedly not reassembled, right, I could buy that, But three since that haven't been an accident, so it's kind of weird. But I'm off subject.
The problem with air conditioning, to speak directly, is is it animal, mineral or vegetable Is it chemical? Is it
out of refrigerant? Is it electrical? Is it not getting
proper signal? Is it mechanical? Did a component fail? And
and that's that's really what you're setting about to do for somebody to say, hey, my AC isn't cooling? That
is that is the most difficult condition to diagnose. Where
do you start? I always do it like this. And
someone assured me this week that I am a very sequential thought process human being, and I would have to agree with that. They said, you're always ABC D and
E in. You don't do a to E and I don't.
I always go through the process. First thing I did,
I got in the car, check engine lights on. Okay,
quick show of hands. How many people are going to
scan this car for fault codes for an air conditioning problem?
I am? I did you know what? I found out?
The check engine lights on for nothing related to air conditioning. Well,
there was one chance there was a catalytic converter fault code at P zero four thirty. There was an evaporative
emission's fault code a P zero four forty. And in
all my years, I've never seen a connection between those two with each other or an air conditioning problem and there was a P zero one twenty eight thermostat rate of rise. Yeah, maybe I've seen overheat conditions cause air
conditioning to be commanded off. You know, what's the software strategy.
I don't memorize strategy unless it becomes a very very common pattern failure, and then okay, I recognize it. So
one of the first things I did was I recorded all the codes. I recorded, I reported everything, I sent
it out to a report. I captured the freeze frame.
I captured all the data that when all those problems occurred, even though I'm just gathering data, testing and diagnostics. Cleared
the codes and no air conditioning operation. Okay, Next, hook
the set of gauges up. Hook the AC machine up. Actually,
now this is a twelve thirty four YF car, so there's a very small amount of refrigerant in this This took about twenty ounces of refrigerant, and in comparison on a comparable one thirty four the older style refrigerant as we've come to call it now equipped vehicle, that would likely have been thirty to thirty six ounces of refrigerant.
So it's it's they've cut the capacity of the system way down. Well, there was very little refrigerant there judging
by the gauges just about came up. They just showed
a whisper of pressure. Now, refrigerant loss is interesting, and
you do enough of these over the years, you kind of see one interesting fact is and that is that you can't trust anything that you're seeing. Is that is
that enough of a discharge that did it lose it?
And is it a leak? It's got to be a leak,
you're thinking to yourself, or is it just attrition over time?
Because this isn't eleven going on twelve year old vehicle. Again,
I know nothing of this vehicle. First time I've ever
seen it. Recovered what little refriger there was in there,
and I bet I didn't take two ounces out of this.
So right away I'm thinking leak. But it's always funny.
They always get down to this certain point and then they stop leaking. And I've seen this with tires too.
You ever get a tire that leaks and it gets down the twenty eight pounds and that's it. All of
a sudden, the leak is fixed. It never leaks, It
never leaks less than twenty eight, but it won't hold more than twenty eight And you say why, And it depends on the pressure leak and how it comes together and folds over and seals itself. So I pulled vacuum.
I had no more refriger in it, and I pulled a vacuum on the system and it pulled down into a perfect, beautiful thirty inches of vacuum, pulled it into a vacuum state deep and it stayed there for about three and a halo a half hours. I just once
the machine reached the bottom, I just turned it off and monitored it over the rest of the afternoon. Never
saw that vacuum gauge move even think about moving. I well, okay,
it holds vacuum. Called up talk to the repair shop.
I said, here's what I know. I said, I didn't
have any refrigerat. I've got a couple of fault codes
on this one hundred and thirty eight thousand mile older jeep.
You know, does the customer really want to fix it?
You know, we've got to ask that question. We're obligated.
It's eleven going on twelve years old.
You know.
Right now, all I know is it has no or very little refrigerant charge left in it. You know, I've
got to blow a charge in it. I've got to
see what happens when I put a charge in it, or I'm going to put CO two in it and diagnose the leak. And the reason I say CO two
is because to blow a charge of twelve thirty four yf into it gets expensive. It's an expensive refrigerant. It's
probably thirty five to forty percent higher in cost than traditional one thirty four. So let's try doing the the
most effective, inexpensive way we can repair shops. Decision No,
blow a charge in it. Customer will see how long
it lasts. We'll see how long it goes on. They
know their customer, they know what they want to do.
I'm just taking orders and filling baskets, no problem. Blow
a charge in it. Hour later. Hey, the air conditioning
doesn't work in the jeep. Compressor doesn't turn on, but
it's got a charge in it. Ran around with a
black light real quick. Even though I didn't expect to
see anything, and I didn't see any leaks. I had
mentioned to them prior that the AC condenser. The condenser
is the piece that sits behind the grill in front of the radiator, behind the grill in front of the radiator.
It takes all the road rash, all the crud, all the junk from the road blowing up on it. You're
driving along at eighty eighty five on the Interstate, and that you're right in the tail that eighteen wheel or all that those little rocks are getting thrown into the condenser as well as the windshielding and those of the car.
You know, I often think about that rock chips only happened when you're doing one hundred miles an hour or more.
But that's a hot rod story for another day. So
what do you want to do? Well, diagnose why the
AC doesn't come on? Oki Doki. So I let it
sit overnight. It was late in the day at that point.
Came in the next morning and listen, how complicated you want to make this? Started the truck up, Bang, check
engine lights back on again. All right, let's see what's there.
EVAP fault. It failed EVAP overnight because the EVAPP ran
overnight when the vehicle was off. It's a key on
engine off monitor for EVAP and it set an EVAP code.
Don't care, it's got nothing to do with my air conditioning.
And I said, you know what, Let's go right to the source. While I had the scan tool looked up
looking at codes, I went into the body computer and the engine controller and I turned the AC on them.
I could look right on the scan tool, AC request off, bank hit the button AC request on. Okay, so I've
got the command. The command is coming through the computer.
It's replaying it back to the scan tool. I can
see that the button works, the dash works. I tried
functional test. There's a functional test where you can manually
overwrite everything and turn the AC compressor on. Nada, nothing.
ZIP got out a wiring diagram just for giggles, and I saw that everything ran through the power distribution center, which I kind of expected. But I said, you know,
it's a simple two wire compressor, twelve vaults in ground.
So I got out the tongue in cheek, he says, with a smile on his face. Most singularly expensive piece
of diagnostic equipment I have in the shop, and it's about twenty eight years old. It's a seven inch round
style headlamp. That's it off of an old actually I
think it's off of an old Chevelle. And I measured it.
It pulls about a seven and a half to eight amp blow depending upon the day. And it's great as
a load substitution. Disconnected the AC compressor. Wired it in
as nice as you plead, please with some some wires and connect clips that I keep around the shop. Turn
the AC on. Bang, headlight turns on. Okay, you got
a bad compressor. I so here's a system that was empty.
Here's a system that needs a compressor. And I said,
you know, it's been twenty four hours. Let me go
down and look at that bottom of that condenser again.
And I get down. I turn off the lights in
the shop. Well, actually I turned off the lights in
the shop. Surprised Danny because Danny was doing something. Oh sorry,
I'm turning off the lights. Danny was in the dark
there for a minute and got down, glasses on, looking through with a black light, bottom of the condenser shows green.
Dye.
Okay, turn the lights back on. Got Danny back to work,
called up the shop. Hey, guess what. I have good
news and I have bad news. The good news is
I know why the AC doesn't work. The bad news
is it's the compressor. Oh and by the way, the
condenser's leaking, so it needs a compressor. A condenser, probably
a catalytic converter, some sort of evap diagnosis, and the thermostat the twenty fifteen jeep of one hundred and thirty eight thousand miles probably needs seven or eight grand worth of work by the time you start agging it all up.
But that's not what I'm there for. I'm there to
just diagnose the AC, not pass judgment. Now, Tom and
I were talking about this before the show today and Tom said, well, isn't it time to just get a new vehicle? And I said, you know, Tom, I don't
know the answer to that question. I don't know what
sort of service and maintenance was done to that question. Now,
Tom Ray, my executive producer, chief cook and bottle washer that pays attention to me, he brought back the correct question.
He said, what's next, what if? And what's next? And
I said, right, I said, but what maintenance has been done?
And that's what I want to know. The point is,
estimates are tough to write. An estimate is nothing better
than an educated guess, especially in the world of AC.
But in the majority of times it's an educated guess.
I think an estimate really helped prepare you the customer you know, grit your teeth and showed determination. Charlie Brown,
can you get through the ex of this repair or not?
I'm not sure what they're going to do to fix the jeep. I'm not sure if they're going to fix
the jeep. The shop took it back. They paid me
for my diagnosis, and we'll see it may come back next week so we can recharge the system for them.
They don't have a twelve thirty four YF machine and time marches on estimates air conditioning. Boy, sometimes the two
just don't seem to go together. Eight five five five
six oh nine nine zero zero. I'm running Indy in
the car doctor. I'll be back right after this.
Where you're vehicle not taking you where you want to go, Well call Ron. He's the expert at making your vehicle
take you where you need it. Eight five five five
six zero nine nine zero zero. And now back to Ron.
Hey, let's go down to Tennessee and talk to Emmett. Emmett,
what's going on? Running the Indie in the car Doctor
at your servicer?
Okay, I've got a note here and I'm gonna read it to you, and then if I leave something out that's for you to tell me what to do. First off,
I put a big hammer near the toolbox and I call it my attitude adjustment tool. But anyway, it's a
twenty sixteen Kia Soul plus two liter in a direct injection, no turbo check engine like it popped on. I took
it to AutoZone. They diagnosed it as a P zero
four to four zero, I think the first time canister.
Let's see here the per Solinois valve. They said. I
didn't want to leave without a part, so I bought the part. Then when I got home, I went online
to doctor University Google and found out what was going on.
Did the check with the twelve oll that either you apply twelve to it, it closes it you whatever, And yeah it worked, so really I took the old one out, checked it and I believe it was working. But I
replaced it. Anyway, I at that time went to a
TVC valve. It leaked, suck and blow test leaked about
eighty about held eighty percent. You could tell a smaller leak,
just a small leak. So I replaced it. Before I
put it in. That one checked tight suck and blow.
Everything was fine. I go about my business I run
Exxon fuel standard octane regular gas and four or five tanks.
The light pops on a P four four two. So
at this point I take it to a friend who's a good mechanic. They do all kinds of checks, smoke
checked it. Everything was fine, and then we sat down
scratched our heads. What should we do next? So I
looked around. He's a drag racer, and he says, you know,
I've thought about this a lot since you told me about it. I'm wondering if it's manner is the fuel
vapor pressures are affecting that the computers and they're throwing codes.
Because when I fuel up and have a tank of fuel, I'll get up to thirty one to thirty two miles to gallon. I drive ten miles to the house, it's
dropped one or two miles. The next morning that's still
that's say thirty one miles to gallon. I go twenty
miles down the road and it'll drop down to twenty eight three, twenty eight five and slowly over the tank of that fuel increase up to thirty thirty one miles to the gallon.
EMMETT stop there in I don't know in more years than I care to remember. I've never seen a correlation
of EBAP system leaks against fuel economy. So we can
go down that road, but with all respect, we're gonna go into analysis paralysis. Right, So let's talk about evaporative emissions,
all right, because you're you're in the neighborhood of evaporative emissions and system failures. Do you understand what evap emissions
is about? And I don't say that to embarrass you,
I say that as a general question. Do you do
you know what they're looking at, or testing or concerned about with regards to the evaporative emission systems of a vehicle.
Well, my understanding is you're you're picking up that they're directing the fuels up to the intake manifold so they get reburned.
Well, that's part of it. And it's not that they're
putting fuel. They're putting fuel vapor, all right, vapor. But
the idea is this, take a take a gallon gas can, right, and you know you're going down to the local story, local gas station. You fill up your gas can with
a gallon of fuel, and you put it in the driveway in the hot sun, sealed up what's gonna happen to it?
The tank is gonna it's either gonna blow the cork off or you can see the tank expand.
Right, it's going to bulge. Right, So aren't automobiles really
like that gas can? You think about it? Right? So
we've got to have a way to vent pressure from the gas tank out to the atmosphere. But if we
did that by traditional methods, well in the old days, we would have violated the Clean Air Act. I'm not
sure anymore, but the idea is we would be violating the Clean Air Act of putting harmful emissions into the atmosphere.
So the onboard vehicle has a charcoal canister that, at the proper time, based on tank pressure and fuel temperature, will open up a vent valve and allow fumes to transfer out to the atmosphere via the charcoal canister. You're
with me, Yeah, all right? You sit tight. When I
come back, we're going to do a deeper dive and talk a little bit more we'bout evapp. But this really
comes back to I want you to understand how evapp works before we talk about the potential cures and some of the quick checks you can do here so don't go anywhere I'm running any of the car. Doctor. We'll
be back with EMMITTT from Tennessee and is sixteen kia right after this. Yay yay from the city streets to
the open road. If your run needs help, run, we'll
keep you rolling.
Right.
Here's a card, doctor, Doctor car invist.
Emmitt. You there, sir, Emmitt, Yeah, oh, there you go.
So when we took the pause, we were talking about evap, right, We're talking about the dangers of a sealed gas tank and how it could rupture and expand, and so we have to find a way to vent those fumes. Right, yeah,
So on a car, there's two devices. There's a purge
valve and there's a vent valve. Purge valve is in
the front, vent valve is in the back. When they
want to, they'll open up the vent valve. They'll run,
allow fumes to vent out of the tank to reduce pressure through the charcoal canister to clean things up, and that cuts back on pressure and prevents the tank from bulging, exploding, et cetera, et cetera, et cetera. Right when the engine,
when the engine is running at select times, they will open up the purge valve, they'll close the vent, they'll open the purge. Sometimes they open the vent to allow
air to pull through, all right, and they will take those fumes and scavenge or vacuum out the canister if they feel it's got too much fumes in it, so they don't overload it and it gets oversaturated.
You're with me, yes, sir. You know.
Think of it as if you live in a house with a front door and a back door.
Yep.
If the air is stuff, you open up the front door.
If you want air to pass through, you open up the front door and the back door. Front door is
the purge valve. Back door is the vent valve. Depends
on the condition, depends on whether temperature, a bunch of factors. Now,
the one thing we haven't added to our evaporative system yet is and the question you got to be asking yourself, how do they know when it's the right time to do anything?
Right?
Yeah, So they add something called an FTP, a fuel tank pressure sensor. All systems have it, and they look
at voltage. It's a variable resistor. It's a variable voltage signal.
Typically at rest keon, engine off, you'll see about two and a half volts out of most of them, and then as it pulls it into a vacuum state, it'll go down, and as it goes into a pressure state, it'll go up. All Right. The reason they have it
at two and a half volts is that's kind of middle of the road, right, If it's a zero to five volt scale, two and a half vaults is middle easy to remember, right, So at select times they're gonna pull they're going to try and vent the canister. At
certain times they're going to try and pull fumes into the engine. A four to four You started out with
a four to forty folt code, right, P zero four to forty, which is a general EVAP failure. Change the part,
Now you've got a four to forty two? Right?
Right?
Do you still have the old part? I believe, Do
me a favor, put it back on the car. Okay,
you changed the purge valve, right, yeah, okay, do me a favor, put it back on the car. Let's let's see.
The first thing I want to know is does the P zero four to forty come back because the code changed?
It changed when you changed the part. Did firing the
parts can and create the issue? And now it's going
to take you down a dark path, right and make you think there's more problems here than there actually is.
Once you get that original purge valve back on the car.
The purge valve we're talking about is in the front up by the engine, correct, correct?
All right?
With I want you to electrically disconnect the purge and you know the rubber hose that led to the back of the car. Yes, that's the hose that the fumes
came from out of the canister. Starting to make sense, Yes,
all right, with that valve electrically disconnected and the engine running, should we have vacuum at that inlet side to the purge valve where the hose is disconnected? What do you think?
No, you wouldn't have any right.
When will we have vacuum there.
When you connect the hose and the valve opens?
No, when you electrically connect the valve electrically Okay, right?
And I said it like that for a very specific reason.
That valve is commanded open, capiche. Yes, So, so if
we start the car and I do this with a rubber glove on, I I wet the end of my finger and I'll just stick it over the end of the purge valve with the engine running, and I'll do this when the engine's cold. I'll do this when the
engine's warm. I want to see if it changes with temperature.
And if my finger is sucked towards that purge valve in the least little way. What does that mean?
That is the valve is open and you're pulling the vapors into the engine.
Right, that valve is leaking. Right if it's electrically disconnected,
there's no way that valve can make can or should mechanically be open.
Right, Okay, I see what you're saying.
Right, the front door is leaking. The wifes can plain
and emmett it's cold in here, close the door, right, So there's there's no way that's that's working. Now, if
you go put your replacement perge valve on and you get a different fault code, you know what that means.
The new perge valve is no good. You know it's
it's it's we're dealing with two different things here because the parts canon got fired. So I want to baseline
this car. I want to diagnose. A fault code isn't
a diagnosis. A fault code is gathering information and I'm
stressing that for you and everybody else listening today because that's the reality of it. Nowhere in a P zero
four forty two or four forty or four fifty six or any other fault code, does it go You've got this code, change that part. There's multiple steps to consider.
There's multiple ways that that code gets triggered. All right, Okay,
Now to do a deeper dive into EVAPP. Let's say
that perge valve was connected, and it's electrically connected, and it wasn't being commanded on right right. So if I
had a scan tool and I looked at the fuel tank pressure sensor and it said two and a half volts, and all of a sudden, I'm looking at it and I see it go to two four two three two point two one point eight. Wait a minute, I'm not
commanding the purge valve on. What does the computer think?
Incorrect purge flow? Right?
Right?
It's not electrically commanding it on, but it knows because it looks at FTP it says, hey, wait a minute, how's the voltage changing? And that's why and that's why
we test, because could I have a shorted FTP sensor? Sure?
Could I have a bad purge valve? Sure you know
there's there's a couple of scenarios. Could the ground wire
for the purge valve be shorted against something metallic and closing it and pulling the purge on if there's power to it all the time. Sure you see the danger
in just swapping parts.
Well, I'm a full believer the swapping parts. And that's
what bothers me about technicians. A lot of them read
the codes and then they go and see what the parts are recommended or a possibility yep, and they start changing parts. They don't go further and diagnostic.
Right, that's right, absolutely.
And I'm not I don't have a scanner. Nope, I'm
not a brainiac or a computer guru. But like I say,
I try to figure out why it's happening. Then if
you figure that out, then you can correct it.
Right. But that's what I want you to do. First.
I want you to go look at purge. I want
you to test it the way I described it, and if that purge is working, leave it alone. Then we'll
have to talk further. I want to see what code
comes back. I want to see what this develops into.
This could be a bad Hey, can the front door of your house leak? Can?
Can?
Can the back door of your house leak?
Right?
You know there's there's just a bunch of scenarios. I
want to see what fault codes are truly occurring? All right?
How many miles are on this.
Kiya ninety ninety three thousand.
Well, the honest answer is it's all bad. But let's
try and diagnose it anyway. All right, but do those
changes for me. Call me back next week or the
week after. Let me know what happens.
Yes, I got one question real quick, velvelean, restore, and protect.
Have you had any experience with that oil? No?
But you know, just because I haven't seen it doesn't make it good or bad. I think that there's a
lot of good oils out there. I think that oil
technology has really closed the gap on who makes the best oil. I think the best oil is the oil
that's changed on a regular basis, and I think there's a lot to be said for that. I think some
oiales are better than others. But just know that, all right, Kitto,
I can't wait to hear from you. Let me know
what happens. Emmett, I'm run any in the Car Doctor.
We're back right after.
This Phil in Massachusetts.
You're up next on the Car Doctor. How can I help, sir?
I got on w show. Listen to what every week.
I've learned a lot, Thank you. Okay. I got a
twenty eighteen sorrent though it's a three lead, a six cylinder, OH wheel drive, forty five thousand miles on it, and I changed oil every five thousand, and he rotated the tires, got new ties at twenty eight thousand, and had one accident.
I was sideswiped on the front passenger side about three years ago, and that was repaired at a body shop.
So that's the history. Do you have any I have
two issues in one question. My first issue is a
consistent rattle or thump evident when I drive at low speeds and it's at the same frequency. You know. I
was due for an oil chair. As I brought it
to my local mechanic, he took it for a test.
He re created the sound, you know, he heard it, but he could find nothing wrong. So he says, I
can't find anything wrong. There's nothing loose suspensions. Okay, the
tires are good. He advised me to take it to
a dealer. I'm just looking, you know, he he he
only does like no more maintenance will changes?
Well?
Right side or left side of carfell if you were to guess.
Yeah, proximally passion this passenger side center?
Okay, so do this is it? Is it there when
you hit a bump? Or is it there just driving along?
Just driving along and I can hit it at low speeds?
All right? Does it change if you hit a bump?
Don't know?
All right? So if we take it out on the
road and you got to look for you gotta look for the right road, if you know what I'm saying.
You know, if we were at the shop, I tell you it's Smith Street because I make good head up the Smith straight, I make a right. There's this little
whoopedie do in the middle of the road that if I catch it just right on the left, if I catch it just right on the right, I can always put one side of the car in the pothole, if you know what I'm saying. So if it makes it
on the left and not the right, I know it's the left side. Then when I go back to the shop,
I'll be slow going into the driveway and as I roll into the driveway. We always we made the lipt
to the driveway a little bit bigger, and I use it for diagnostic purposes. If I hear it when I
hit the front tire, I go, okay, it's left front.
If I hear it when I hit the back tire, I know it's left rear. At least it gives me
a direction. If it's nothing, if it doesn't matter when
it hits a bump, if it's just there while I'm rolling along, then I'm going to start looking at different things.
I'm gonna start thinking about heat shields. I'm gonna start
thinking about things that are dangling in the wind. One
of the dangers or problems and trying to diagnose a noise on a traditional lift where they're supporting the body and the suspension hangs free, is if there's something loose, the weight of the suspension is pulling down and it might be hiding whatever's rattling. So a drive on lift
is probably the best thing to use. But that's that's
how I would approach it.
Second question, Okay, this one may affect my wife's safety the she sits on two cushions on the passioner's seat, Because you know she's shorter than I and I'm not even tall, so and it's everything's been fine. But about
a year ago, the passenger airbag off light stays on.
I tried removing the pillows and her sitting on the on the passion seat, and it still stayed on. I
tried her readjusted her weight to make sure she was putting her weight in the seat, and it stayed on.
Soh you know, so I know by Oko mechinicate, you know, he couldn't figure it out. So he again advised to
go to a any ideas on that is the light still on, still goes on and stays on.
Okay, I'll tell you what. Let me pull over, take
a pause. When I come back, we'll come right back
to you. We'll be back with Phil. I'm running Indie
in the car. Doctor. We'll return right after this ron
An Indie in the car Doctor here for the final ride this hour. Let's go back to Phil and mass.
Phil. You're there, Yes, I'm here.
So you know that eighteen Sorrento, if the airbag light is on, there's a fault in the system. Has anybody
scanned this for codes?
Not yet?
Okay, so let me ask you a question. How long
ago did this happen?
This happened about six months ago.
All right, does your mechanic I'm not picking on your mechanic.
I'm just curious. I hear this a lot. Does your
mechanic own a scan tool?
Do you know? You know, I do not know. Like
I said, he's always done new team maintenance, you know, right, well.
But here's my point. All right, and listen, you and
I are just having a casual conversation. I Am not
trying to beat anybody up. I'm just trying to make
a point. You know, I just went for a dermatology exam,
and and I went through the whole exam. They looked
me overhead to toe literally, and there's nothing wrong with me.
And there was nothing wrong with me, he says, I'm in great shape. And the insurance company paid a whole
lot of money for that test. So you know, why
wouldn't you when you go to your mechanic, if he owns a scan tool, and most of it, most most shops have to have a scan tool today even to do general maintenance. All right, whether it's brand X, Y
or Z. And in that scan tool, I can almost
guarantee you there is the capability to do a complete system scan. Wouldn't Phil be willing to pay? I don't know.
Would Phil be willing to pay fifty seventy five one hundred bucks to have a scan done of the car? Hey? Phil,
it's it's this particular fault. I can't fix it because
I don't have the rest of the tools. But at
least when you go to the dealer or you go to the next specialist, you at least you know what you're looking for. Wouldn't that make you feel better? Isn't that?
Isn't that kind of like going to the dermatologist and getting a skin exam, right, sort of the same thing.
So somebody's got to do a scan to this car, Phil, somebody's gonna have to look this car overhead to toe and determine why that's like that. Be aware if that
airbag light is on, that means in the event, God help us of a collision, the airbag will not deploy and your wife will not be protected. It's not because
she's sitting on cushions, because the air bag is not gonna come out. So let's get it scanned real quick.
I'm not an ady in the car doctor until the next time. Good mechanics aren't expensive, they're priceless.
See ya, Hey the car Doctor, Car Advice to ride
About this episode
Ron Ananian tackles a “double whammy” Jeep AC failure on a 2015 Grand Cherokee: the system had almost no refrigerant, then after recharging the compressor still wouldn’t run. He walks through his diagnostic sequence—scan codes, verify charge with gauges and vacuum hold, then confirm the AC command from the body/engine computers. With a clever headlamp-as-load test, he isolates the compressor as the culprit. A blacklight reveals dye at the condenser, meaning the condenser is leaking too, so the repair likely involves both parts.
A simple A/C complaint on a 2015 Jeep Grand Cherokee quickly turns into a lesson on why repair estimates are only educated guesses. Ron explains how one failed component can uncover several more—and why proper diagnostics always come before replacing parts.
Also this week, Ron helps a listener solve a persistent EVAP system fault on a Kia Soul, explains why testing beats guessing every time, and answers questions about suspension noises and airbag warning lights.
Real diagnostics. Real repairs. Car Advice, Done Right.
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