Your car’s computer constantly fine-tunes the fuel it injects. If those adjustments keep changing, it can mean something is wrong even when there’s no warning light.
This system keeps gasoline vapors from just venting into the atmosphere. If it’s not working right, it can cause problems that you might not notice right away.
The EVAP system is how your car keeps fuel vapors from escaping. The car also runs a test for it, but that test only happens when conditions are right—like having a certain amount of fuel in the tank.
The thermostat helps control how hot the engine runs. If it’s not regulating temperature correctly, the engine may run less efficiently and burn more fuel.
Wheel speed sensors tell the car how fast the wheels are turning. If one sensor fails or cuts out, the car may not know the correct speed and some braking/traction systems can act differently.
An AGM battery is a specific type of car battery. It’s designed to handle vibration better and can work differently than other battery types, so matching the type matters.
A flooded battery is the more traditional kind of car battery with liquid inside. It behaves differently than AGM batteries, so you shouldn’t swap types without checking what your car needs.
A Toyota Tacoma is a popular midsize pickup truck. Here, the caller’s 2009 Tacoma is having engine misfire problems, and they’re trying to figure out what part is causing it.
The ignition coil makes the high-voltage electricity needed to create the spark in the engine. If the coil isn’t working right, the engine can misfire on that cylinder.
Fuel injectors are responsible for spraying fuel into the engine. If they get dirty or clogged, the engine may not get the right fuel, which can cause misfires.
A diagnostic trouble code is like a specific error message stored in the car’s computer. It helps you and a mechanic figure out what system is causing the problem.
Term
OBD-II scan tool
An OBD-II scan tool is a device that connects to your car and reads the computer’s error information. It helps you see what the car thinks is wrong, like which cylinder is misfiring.
Your car’s computer constantly tweaks how much gas it injects. If it has to keep changing that a lot, it can be a sign something is wrong—like a sensor or an air leak—so the engine isn’t burning fuel the way it should.
A valve is like a door that opens and closes to let air and exhaust in and out. If a valve gets damaged or doesn’t seal well, the cylinder can lose compression and start misfiring.
A misfire is when a cylinder doesn’t light off the fuel correctly. That makes the engine run unevenly, and the car’s computer can often detect it by watching how the engine speed fluctuates.
Crank speed is how fast the engine’s crankshaft is spinning. If a cylinder doesn’t fire right, the engine speed can dip slightly, and the car’s computer can use that pattern to spot misfires.
P0301 means the car thinks cylinder 1 is misfiring. That’s useful because it points you toward problems that affect just that one cylinder.
Concept
carbureted engine rag-over-carb smoothing
On older carburetor cars, people sometimes tried blocking airflow to change the fuel mixture and make a rough-running engine seem better. The point here is that modern cars don’t do that—they monitor mixture electronically.
The valve train controls when the engine’s valves open and close. If the misfire happens mostly at idle, it can sometimes point to something mechanical in how the valves are working.
The EGR valve helps control emissions by sending some exhaust gas back into the engine. If it gets stuck open, the engine can run badly because the air/fuel mix and airflow aren’t right.
Live data means the scan tool shows what the sensors are reading right now. Instead of guessing, you can watch if the readings make sense while the problem is happening.
The Chevrolet Sonic is a compact Chevy. The host is talking to someone about a Sonic problem, and the key idea is using a scan tool to check what the engine/emissions systems are doing.
A turbo is a device that uses the car’s exhaust to push extra air into the engine. More air can help the engine make more power, but it can also cause problems if the turbo or related parts aren’t working right.
Rough idle is when the engine shakes or sounds uneven while the car is sitting still. It can happen when the engine isn’t getting the right fuel/air mix or when something is misfiring.
Running rich means the engine is burning more fuel than it should for the air it’s getting. That can make the car run rough, like it’s stumbling or sputtering, especially at idle or when coming to a stop.
A complete scan is when a mechanic plugs in a computer to read what the car’s engine computer has recorded. It helps find the real cause of the problem instead of guessing.
The check engine light means the car’s computer noticed something wrong. It might not feel terrible right away, but it’s still worth checking because the computer can save clues about the problem.
Sensors are the car’s “measuring tools.” They collect information about what the engine and vehicle are doing, and the computer uses that information to decide what to do and what might be wrong.
Your car runs built-in tests to check whether systems are working right. After the codes are cleared, it has to run those tests again to see what comes back or what else it finds.
Concept
accumulative damage
The idea here is that if a problem has been going on for a long time, it can lead to bigger problems later. Even if the car still runs, the faulty condition may keep causing extra stress.
P0128 is a code the car’s computer stores when it thinks the engine isn’t warming up properly. Often it points to a thermostat or coolant-temperature problem.
“Lockout” here means the car’s computer stops doing certain checks. If conditions aren’t right (like the engine running too cold), it may refuse to run its usual tests.
Self tests are the car’s built-in checks. They help the computer confirm whether sensors and systems are working, and if they don’t run, problems can be harder to detect.
The purge valve moves fuel vapors from an emissions charcoal canister into the engine. If it’s not working right, the engine can run rough or sputter because the vapor flow isn’t correct.
“Code scanned” means plugging in a scanner to read the car’s error codes. It helps the mechanic see what the car noticed, not just what you feel while driving.
In automotive electronics, power and ground are the supply rails that keep a module operating correctly. If a radio has constant power and ground but still misbehaves, it points away from simple wiring issues and toward an internal fault or module failure.
An aftermarket radio is a replacement stereo that isn’t the one the car came with. In many cars, it has to be wired and set up correctly so it can “talk” to the rest of the car’s electronics.
CAN is the car’s internal “data network,” kind of like how different electronics communicate. If you change the radio or wire it incorrectly, it can cause other weird behavior because the car expects the modules to work together.
This is a voltage check: the mechanic is confirming the circuit is getting power from the battery. If that power isn’t present, the computer or starter-related parts won’t work correctly.
Cars need a good electrical “return path” to ground. If the ground signal is missing or weak, the computer can’t properly control the starter or other systems.
Code retrieval means reading the car’s stored error codes. Those codes can help narrow down what system is failing.
Term
FOLT codes
Fault codes are the “error messages” the car stores when it detects a problem. If a scan shows none, it can mean the car isn’t communicating properly or there’s no stored fault.
Term
complete system scan
It’s a scan that tries to read trouble codes from different car computers. If it can’t pull anything, the issue might be communication between modules, not just a bad sensor.
It’s a plug-in adapter for the car’s diagnostic port that lets you test the signals with a meter. Instead of guessing what’s happening under the dash, you can measure what the scan tool is seeing.
The OBD-II connector is the port where mechanics plug in a scanner to read trouble codes. If the scanner can’t talk to the car, it can point to wiring or communication problems.
CANbus is the car’s internal messaging system between computers. If it’s not working, the scanner may not be able to communicate with the car’s modules.
“Reman” means a rebuilt replacement part. They’re asking whether the computer was rebuilt by GM or by an aftermarket company, because that can change how it needs to be programmed.
Term
aftermarket remen
Aftermarket reman is a rebuilt replacement part from a company other than the original maker. It may still work, but it can require different programming or may not match what the car expects.
A wiring diagram is like a map of the car’s electrical connections. It helps a technician trace which wires and plugs connect the car’s computers and sensors.
In automotive diagnostics, “modules” are the car’s individual control computers (ECM, BCM, etc.) that each handle a specific set of tasks. When diagnosing CANbus problems, technicians often identify which module is “pulling down” the network—meaning it’s causing communication to fail.
In this context, “program” means installing the correct software/calibration and/or performing immobilizer/security alignment so a replacement module can work with that specific vehicle. Even if the hardware is identical, a module may not function until it’s properly programmed for the car’s network and security setup.
Term
key cylinder
The key cylinder is the ignition lock assembly that houses the mechanical and electrical components used to recognize the key and start authorization. In modern cars, it’s tied into immobilizer/key-related electronics, so faults can look like broader communication or programming issues.
The body control module is a computer that runs a lot of the car’s convenience and body functions, like lights and door locks. If it can’t talk to the rest of the car, those features can malfunction.
The EBCM is the computer that controls the car’s braking electronics. If it has a short, it can mess up communication with other car computers.
Term
jumping pins
“Jumping pins” means temporarily connecting two points (often with a jumper wire) to restore or test communication on a circuit. Here, the host uses it as a troubleshooting method: if communication returns after jumpering the network wires, it suggests the original module (EBCM) is shorted or otherwise interfering with the network.
Engine knock is a bad pinging/knocking sound from the engine. It usually means something about combustion isn’t right, and it can be a sign of serious trouble.
In this context, “theft” refers to the vehicle’s anti-theft/security mode. When the car detects an authentication or communication problem, it can lock out starting or trigger security-related behaviors.
Brake fluid is what makes your brakes work by transferring force through the brake lines. DOT 3 is a specific brake-fluid type, and if a batch is contaminated, it can make braking less reliable.
A non-compliance recall means the product didn’t meet required safety rules. Here, the issue is brake fluid that may be contaminated and could affect how well the brakes work.
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Now start your engines. The Car Doctor is in the
garage and ready to take your call.
You know, I want to go back and talk real quick before I go to George and Alabama about fuel trim's or fuel economy once again. You know Memorial Days
coming up, right, because there's a couple of things I didn't touch on in the last show, and you know it's it's it's sort of simple conversation, right The issue is we all look for faults when they occur. We
don't look for preventative things. We assume if there's no
check engine light on the car is good, and that's not true. You know, fuel trims can drift a little bit.
There can be problems with the evaporativision emission system. For example,
if you always fill your car up at the three quarter tank mark, you will never ever set an evaporative emissions fault code. Did you know that? And the reason
is because the EVAP monitor. The self test for the
EVAP monitor runs at three quarters of a tank or between three quarters of a tank and a quarter of a tank. So consequently, if you're the other way around,
if you're putting in three dollars well let's make it five dollars a trip a gallon every time you take take the car out, because you go down to the corner store and there's always less than a quarter tank, it'll never run the EVAP monitor. So you cant have
a problem with the evaporative emission system where it's venting fuel and fumes over the time, that's gonna cost you fuel economy. Maybe the thermostat's running cooler now, depending upon
how you're driving. That thermostat fault code may not come
up so quick, so you may use more fuel. And
maybe once in a while a wheel speed sensor is dropping out and it's affecting the way breaking operation occurs, affecting actual calculation of vehicle speed. So the point is,
if we're looking for fuel economy modern cars, you know, they're like that walk in the woods.
Right.
Was it Hansel and Gretel that dropped the breadcrumbs along the way and to find their way back? I think
that was a different fairy tale, But you get the point.
Memorial Day weekend is coming up, and it's a great reminder.
It's a great opportunity to say, pay attention to your vehicle now when instead of on the side of Interstate ninety five with the family staring at you, especially going I told you this is the unofficial start of summer driving season here in America. Right, we're loading up the SUVs,
the coolers are packed, the kids are going. Are we
there yet? You haven't even left the driveway. Everybody's heading
somewhere at once. And trust me, this week, we could
see the traffic in New Jersey was just getting bad.
Check your tire pressure. Check the spare. Look at the battery.
If it's older than four years, you know what are we waiting for? Okay, If it's an AGM battery, put
an AGM battery back in it. If it's a standard
flooded battery, put a standard flutter battery back into it.
Put what's Put the right battery into the vehicle. If
you're trying to pick a battery, get out to auto Batteries dot Com and read about it there. Look at
the wiper blades. You have your peak wiper? Do you
have your peak wiper blade? I gotta said a peak
wiper blades. I put them on the plow truck this week.
Oh my god, it's like night and day. Look at
your fluid levels and listen. If the check engine light
has been on since Valentine's Day, maybe you know you got to stop hoping it's going to fix itself. We're
about to start the summer driving season. Cars don't. Cars
do not heal emotionally. They just don't. They don't magically
fix themselves sometimes short term, but nothing's going to ruin the upcoming holiday weekend faster than standing on the shoulder of the highway of filling your family. Well it didn't
do it yesterday. Well, but you had two weeks to
get ready. Meanwhile, steam's coming out from under the hood.
You know what. You guys spend more time organizing the
cooler sometimes than preparing the car for the trip. So
if the sandwiches are organized and the beach chairs are packed and the dog has snacks, the car deserves a little love too. Just just get ahead of it now
while you can. I'm ronning ay in the car. Doctor.
Let's go and open up the phone lines. Let's go
over and talk to George and Alabama nine Toyota Ta Coma.
See what's going on here? George, Welcome to board, sir.
How can I help?
Oh yeah, let's see. Of course you said it two
thousand and nine to comea with a two point seven fourth cylinder about one hundred and ninety one thousand miles.
A couple of weeks ago, check engine light and attraction light came on, pulled in and had it diagnosed, and it said it was a misfire on number two. Too
many misfires, I guess the whey they read it. So
I went, well, go to the internet. What's the problem. Well,
let's either the plugs, coil or injector according to the simple interpretation. So I went, well, the plugs have about
old fifteen, maybe twenty thousand miles on them, and I didn't want to get into injectors. I went ahead and
replaced number two coal, and sure enough, the next day or two got a missfire on number two. Well, okay,
let's go ahead and get in there. And I've swapped
one in two plugs and put the new coil on number one, and all of a sudden, get a code, Well guess what's missfire and on number one. So I figured, okay,
must be plugged. So I went and bought new plugs,
put those in and got about uh oh, let's see.
While I was in there, I went ahead and bit the bullet and cleaned the injectors, and so got about two hundred miles. And all of a sudden, check engine
light traction comes on and it says I'm getting intermitt and misfires on all cylinders, particularly number one. I'm at
a loss.
Okay, help me wrong. So where'd we get the coil from?
Got it from Toyota?
Okay, So it's a real Toyota coil.
It is a Toyota cold, all right.
When the misfires occur, do you have a scam tool that we'll read misfires.
After the fact, not during driving.
Okay, it's gonna make it a little bit more difficult, because I'd love to see. I would love to see.
Do I have a fuel trim problem?
You ever?
You ever mold the lawn George?
Yes, sir, you ever?
You know the lawnmower doesn't run right? Why? Why does
the lawnmower not run right? Bad? Plug right?
Usually a plug.
Right, carburetor problem, or something mechanical in the engine right, burnt valve, usually in the head well. And you know,
here's a case where and and for the record, if we were down to where it was occurring on one cylinder, I would have loved to have just taken the coil and put it on one cylinder, and the plug and put it on another cylinder. Which way did the misfire go? What?
What followed?
What?
M all right? What you've done now is and and
I get it. I'm not scolding. I'm just saying, what
you've done now is you've you've changed the parameters of everything.
So we have to we have to think and start over, all right, So if we've got a misfire being reported on all cylinders, I'd sure love to see that live on a scan tool. Yeah, what's what's what's actually going on?
Which cylinder has the worst misfire going on? A misfire
on two cylinders, for an example, can affect the engine in the way that it operates and create what we'll call ghost misfires. They're not really misfiring, but it's affecting
crank speed and causing it to stutter in that hole.
You ever think about how a computer determines whether there's a misfire going on or not?
No, all right, so baffles me.
So you got a kitchen table in your house. Of course,
the doorbell rings, Get up and walk from the kitchen table to the door at at at whatever pace you choose. Right,
that's your that's your pace, that's your that's your that's that's the length of time it takes you. Let's say
it takes you eight seconds, all right, all right, But now you come home from work one day and you drop something on your foot and you're walking with a limp.
You can't do it in eight seconds, right, So, so the length of time it takes you to get to the front door to answer the doorbell. It changes. The
duration of time changes. Right. A crank shaft rotates at
set speed. The computer knows when it fires number one.
It's programming tells it it's going to take it so many milliseconds if you want to say seconds to ease the conversation and not make math an issue. It's going
to take so many seconds to rotate from the first firing event to the next firing event, to the next firing event and so on. And it knows that speed
based on engine RPM, load, etc. Well, if all of
a sudden it's coming around and getting ready to fire, just fired number one, and it's getting ready to fire number number four, all right, and it's supposed to take eight seconds, and now it takes ten. WHOA what happened?
George misstepped? Okay, so it says, hey, there's a misfire
going on here. Depending upon the severity and how how
how consistently that happens, it can become a P zero three hundred, which is random missfire because they can't tell which cylinder is actually missing, or it's going to become an identifying missfire. Three oh one, three oh two, three
oh three, and so on.
That's what That's what I had last time was a P three to zero P three hundred and then uh and P three zero one.
Right now, one of the things I want to see while I'm looking at a misfire like this. You ever
worked on a car in in the older days when it was carbureted and it ran roughedt island. You put
a rag over the top of the carburetor. It smoothed out.
Oh yeah, I got my Studi Baker back here, I'm working on it, right.
You ever think about why that happened? You changed the
fuel mixture, right, it was It was usually dirt and air bleed or something was restricted and you altered the fuel curve. So I want to know, on a modern car,
where's my fuel trim? At idol? Where's my fuel trim
and cruise? When this, when it's misfiring, what's it doing?
In some cases, you know, you can tell take a scan tool, look at data and see, I've got misfires at idol, but they go away off idle. Well, misfires
that go away off idle are generally associated more with either a fuel trim issue or possibly a valve train issue.
A good good point. In fact, once I get up
to speed, I mean it runs pretty smooth, but it does have a rough IDOL and low end.
Right, you know, maybe we've got an EGR valve stuck open?
What years? This is an O nine. I believe we've
got an EGR on this car. If we've got an EGR,
do we have a stuck open EGR valve? So I
think what I want you to do. I'm gonna ask
you to spend a couple of bucks and go buy a scan tool that shows live data. Because, brother, you're
more than mechanically qualify. You got to. I can already
tell you've got enough smarts between your ears. You're working
on older studebakers. You're mechanically inclined. Obviously, that's why you're
here listening to this show. And I think it's time
for you to get a scan tool that just will show you a few things.
Yeah, my son, my son in law that turned me on to you, gave me a nice scan tool and he's talking about, oh, we'll get together and ride and analyze it. And also, right, it has a capability. I
just don't know how to use it.
Yeah, well, I think that's that's where you are, kiddo.
All right, so do that, get some scan tool analysis.
If you have any other questions, you want me ron at cardoctorshow dot com, send me some print out, send me some data, and I'll be glad to coach you a long all right, and then you give us a call back. You let us know what happened up here
on air.
All right, kiddo, you'll hear from me again.
All right, You're very welcome, George anytime. All right, I'm
running any in the car, doctor, let me run. I'll
be back right after this. Hey, let's get out and
talk to Jeff in Pennsylvania fourteen Chevy Sonic do you Sonic? Sorry,
I couldn't resist the Sorry Jeff, what's going on?
Back?
Okay?
Well, sometimes, well I should say sometimes most of the times.
When I'm going down the road, the car runs great, and it has a turbo and that works really well.
In fact, I think it helps decrease my gas knowledge.
But anyways, when I come to a stop, the car will sometimes just start jumping, like bouncing around, and sometimes I put a neutral goes away. Then sometimes it doesn't, so.
That bounces around like a rough idol or like you're feeling vibration.
Well, I'm feeling like the tires are going to come off the ground.
What do you what do you mean like the tires are gonna come off the ground, like the engine starts running badly.
No, it's just the car literally like it. It feels
like it's bouncing, it's shaking, sitting the engine. It's it's
sort of you know, coughing and sputtering, you know what I mean. Sometimes I have to well I put it
in neutral, I have to try to rev it up to get it going again, or put it in park.
So so it'll move it out. It almost feels like
it's like it's flooding out, like it's running real rich for a moment. Yeah, okay, how many miles a right?
How many miles are on this.
There's two hundred and fifteen thousand miles. I'm getting ready
to take it to the mechanic to work on. I
just wanted to see if you could give me a heads up on maybe a potential problem or solution. So
I'm going with a new mechanic, so I don't know a lot about him yet.
Right, Yeah, well, listen, I'm hoping that the mechanic, you know, he's going to say two things to you. Number one,
can we go for a ride so I can experience it right? And number two that he's going to do
a complete scan on the car, whether it's got a check engine light on or not. Does it have any
lights on on the dashboard.
It does have a check engine light on. It's been
on for for a while, and like I said, it's been running pretty good other than this problem. And I
just I was gonna get rid of the car, and I decided to keep it as a as a beater car.
Basically, what do you know what the code is that it's got.
No I have no idea what I had the codes?
Okay, so obviously that's gonna you know, that's gonna be the first step. But here's the catch. How long has
the light been on for quite a while? Six months?
A year?
Two years?
Yeah?
Which years?
Two years? So you ever get hurt in your lifetime
and you kind of walked.
With a limp, I still do, yeah, right, And you.
Notice how your body sort of adjusted for it, right, And even in some cases you got hurt and the injury corrected itself. But you had to you had to
train yourself to walk correctly again, right, and it stopped me.
It stopped, it stopped testing the rest of it. My
point becomes, cars today are smart. Right, So if it's
I don't know, pick a number, ten, twelve, eighteen, how many sensors you think your car has, Let's say eighteen, right, yeah, So if there's eighteen sensors, it's testing every sensor of every moment of every second of operation. But all of
a sudden one of them is a problem. Those automobile
engineers are pretty smart, you know, Jeff. They're gonna say, well,
instead of getting Jeff stuck on the side of the road, we're gonna allow this car to learn. So when censor
A was at this, we know that censor B was doing that, and censor C was this, So therefore we can use calculated values. We don't need to run those
self tests anymore. And here's my point, the fact that
the check engine light's been on for two years, you're gonna have to fix problem A, clear the code, and let the vehicle run its self testing monitors, right, yeah, and then see what if anything comes next. Because what
I'm trying to say is at two hundred and fifteen thousand miles, what's next? What test didn't did run in
the last two years? So what's the accumulative damage that
this could possibly have over a twenty four month period?
And that's so even though the check engine light's been great, arm check engine light's been on, and the vehicle's been running great, there's still tests. I guarantee you it hasn't run.
Let me make it simple. Let's say it's a bad
thermostat P zero one twenty eight, right, and I don't know what it is, but let's just say that the thermostat was allowing the engine to run eight degrees colder than speck, so instead of running two hundred degrees, it ran one hundred and ninety two. That difference is enough
to cause the computer to go into lockout where it won't run self tests. And now there's we'll tell you what.
Sit tight. Let me pull over, take this pause. When
we come back, we'll pick it up from here. I'm
running any in the car. Doctor. We'll be back with
Jeff right after this drama Sety Street. It's to the
open road tonight.
Hell bron will keep you roll.
Do you ever have that moment when you're gonna come back from break? Tom and you're about to sneeze. Is
waiting for you to give me the go to those those those moments happen. It's live radio.
I love it.
Yeah, man, but that's okay. We're here, Jeff p A.
Let's finish up with you. Then I got to get
the Lee.
And Georgia, just because there's something else that might be affecting this also. Okay, when I go and fill up
with gas and then I go and start the car, it just wants to sputter and not run smooth. So
I have to sit there and rev it up, ton't run smooth, and I'm good to take off.
Okay, So you might have a bad purge valve Okay, which which you know? Again? What's the fault code? Have
you ever had the code scanned?
No?
Can I ask you why.
I'm having an issue with the radio?
Say hawk back up? Can I ask why? And the
reason I'm asking is not that is not to highlight you or pick on you. I'm just trying to demonstrate
the value. You know, if it was your leg that
was hurting, why did you at least go to the dock and get it checked out? I would hope.
Right, Well, I did have it checked out, and the person who checked it out said, oh, there's lots of problems and it's going to cost you a lot to fix it. And then I wasn't driving the car for
a while. I mean I was running it, but I
wasn't driving it. And so that's why it's the situation now.
I'd like to drive it again and maybe have it as a beater, and if it's too expensive, I'm just gonna.
Get rid of it right well. And like I said before,
I can't tell you if it's going to be expensive or not because two years with a check engine light on, I can't tell you if it's one problem, three problems, five problems.
Yeah, I understand my faults.
Yeah, yeah, no, And again not to listen. My job
is to educate you guys. But that's the you know,
and and you know, but that's that's the reality of it.
For lack of a better way. You had to comment
about the.
Radio, Yeah, I want to.
I just noticed this. It's like when you're going down
the road, it'll jump to another station. They'll like beep,
make a noise and jump to another station. Or if
you try to get back to it, it might lock up, or it might change different screens on on the screen.
That sounds like from my seat here, if I've got constant power and ground going to the radio, which is what I would monitor on a road test, then it sounds like I've probably got an internal radio fault and I'm gonna send it out to a repair center to have it looked at. All right, but you know, before
you go that routelet's get let's get it running right and and for the record, before you before we go along, well, let me just I'll put an after market radio in it.
I would want to look at the wiring and how is that radio part of the can or the controlled area network system? And is putting an aftermarket radio when
it's going to affect operation and communication somewhere else down the line. So there's things to consider. But let's get
the check engine light resolved first, all right, kiddo. Okay,
so you're very welcome, sir. Happy to have you, Lee Georgia.
How can I help you today, sir?
Yes, sir, I've got a twenty eleven Shay Traverse. I'm
having cranking issues. I've done did everything on your video
that you had posted a while back.
We talked about this car. You and I didn't we
did we? Did we facebook or something? Or we we? Okay,
So so refresh refresh my memory because I remember then, remember the specifics. You went through the purple wire going
down to the starter. You don't have twelve vaults there.
You went to the relay in the jump in the in the underhood fuse block. Do you have do you
have hot at thirty? Do you have ground signal from
the PCM on eighty six?
It's been a while since I've missed with this thing.
I do know that I sent and got a new e CM put in, all right, ordered one, got it put in, and I'm still able to run power jump power from the hot terminal on the fuse block to the yellow wire coming down the fuse block, going to the e CM and it cranks, but no start. But
inside it does not crank, start, don't do anything.
So I'm looking for okay. So the reason that works
is because the PCM is applying power on that yellow and it's constantly grounded at one ten. So what you've
done is you've proved the ground one ten, which is in the back rear corner of the cylinder head is good.
All right, So so that being said, all right, why aren't we getting a signal out of the PCM. Let's
back up a second, refresh my memory. What sort of
code retrieval? What sort of scan tool work? If you've
done with this car?
We scanned it a while back. It comes from it's
been three other shops right, come here, And when she brought it here, she said the motor was knocking already had a warranty motor, but also said it wouldn't crank back up for the other shop. So we tried to
get it to crank so I could hear the knock, and we weren't getting anything, no signal for nothing. Okay,
So most like it's like the like the pat system was messed up.
All right.
So so if you're going in you're making model, right, yeah?
Yeah?
What and what scan tool were you using?
Was it a I got a trite and BT and snap on?
Okay? Right, so you did it. So if you do
a if you do a complete system scan, what FOLT codes do you get anything?
It doesn't give me anything?
Now, all right? So does it communicate with all modules?
No?
It doesn't, it doesn't. So so do we have a
network communication? Full? Right? So if we go down to
the if we go down to the A L d L connector, right, if we go down to the you know, under the under the dash, if we go across pen six and fourteen, what's the resistance? I have not checked
that sixty oms? Got to see sixty oms? Do we
have an open on the CANbus? But see, I'm surprised
if you've got if you've got no communication, all right, do you have a let me back up a second, do you have a OBD two breakup box? You know what?
They're cheap. You'll you'll really love it. Rather than trying
to get under the dash and measure voltage and ground at the ald L connector, you can actually it's it'll actually go between the connector and your scan tool and you can sit there with a voltmeter and monitor voltage ground signal. You can do your can bus check. They're
under two hundred bucks. Brother, They're They're worth every penny
of it. All right, you're gonna you're gonna say how
did you get along without it? Beforehand? But I want
to know if I've got no can communication, If I can't talk, can your scan tool talk to the PCM?
I just can't put it back on. Since we put
the new e c M in, I have not scanned it.
We just tried to crank it. Well, it's got but
it's got deft returnant incorrect.
Right, because because and I was gonna say with with a new ECM in it, did you flash software?
Yeah? I actually got a mobile key locksmith come out
right programmed to feed back to the vehicle.
Well, but how did he communicate with the PCM if it's got no if it's got no communications.
He used some little box in the laptop and actually was talking to it. We couldn't get ours to do it.
So is he is he going through the OBD two connector?
Yeah?
Do you have the other PCM? And did you turn
it in?
Now?
We had to send it back.
One of those moments, all right. So the first problem
is why doesn't the PCM communicate with the scan tool?
Right?
So I'm going to send you down across Penn six and fourteen. Do we have a CANbus problem? Where did
the PCM come from? Was it a GM reman? Was
it an aftermarket remen.
Come from flagships? The PM?
Why that doesn't mean anything to me? Is it a
GM dealer? Is it an aftermarket piece?
I guess they just repair and or reconditioned the computers, the ACMs and send them back.
Okay. Do you have any experience with CANbus diagnostics?
Lee?
Okay, so I want you to get out a wiring diagram for CANbus ever you ever? Does your repair shop
have a computer network in it? You have more than
one computer in the shop?
Yes?
Okay? How many computers you got?
Two?
Two?
So if you had three, all right, and the one in the middle broke, you wouldn't be able to talk to the third. You get that? So, so, which one
of the fourteen modules on this vehicle is possibly pulling down the CANbus? Does that make sense to you?
Yeah?
So?
But now let me ask you this. I got another
traverse the same year, everything identical. I took the ECM,
the body control module, the agnission suites, the key cylinder.
Did you did you program it to your car?
No? No, no, no, We just stuck it into this
one and it wouldn't do nothing right.
Did you program it to that car?
Yes?
We tried to program it to this car and it still wouldn't do anything.
Right because there's a can communication problem, right? Tell you what?
Sit tight? Let me pull over? Take this pause. I
don't want to rush it, but we're onto something here.
I'm running any in the car. Doctor. We'll be back
with Lee right after this. Hey, we're back, but you're
still there. What are you using in the shop for
information system?
I've got I try and Tanner and then the Mitchell software.
Okay, so go into Mitchell right, Go look at you're looking at wiring diagrams. Go look at computer data lines.
All right, and if you understand this, just tell me Ron no wrong path. I'll take it down a different leg.
But I want you to see this first. Okay, go
look at computer data lines. I've only got three minutes.
When you look at computer data lines, you're looking at the network that connects the two computers in your shop, capeche so. So if there's three computers in the shop
and four computers in the shop, every computer is a module connected by a network cable. You're with me, yes,
go look at those computer data line wiring diagrams. When
you go across six and fourteen and they want sixty oms of resistance. That shows integrity of the network because
if you look at it, there's a tan wire and a tan with a black trace. That's the high speed network.
Below speed network, there's an Internet connection and a dial up modem connection. Makes sense?
Yeah?
Okay, So across six and fourteen of the ald L or the OBD two connector or whatever we want to call it in our alphabetized industry, we want to see we want to see sixty omes. If we don't have
sixty omes, why don't we have sixty omes? And then
if we were at the shop, I would I would, I would which side looks more probable to be a suspect?
I would disconnect the electronic brake control module for example.
I would jumper the tan and the tan black to put communication back. Do I now have data communication? Yes? Okay,
guess what I've got a short at EBCM. I don't.
I'm gonna leave it disconnected. I'm going to go on
to the next one. It all depends on the vehicle
and how the network is laid out. I want to
go to the first computer, then the second computer, then the third computer and so on. Makes sense, right? Okay?
I want you to put this car, and I realize you can't put the original PCM back in it because you don't have it anymore. But I want you to
put as much of this car back together as normal as you can, and then start looking at the computer data network. Why don't you have communication on the CANbus?
Last thought? And I just want to point this out
because I just want to make sure I heard this right.
This car had an engine knock before all this started. Yeah,
So before you get buried too deep in this, obviously, I'm sure you have. I've talked to you before. I
know you're a smart guy. You know we may be
fixing a car with a bad engine.
I've got a replacement engine that's going back into the car.
Okay, all right, all right, so then let's fix the wiring issue first. All right, let's figure out why the
computer data lines don't communicate. Let's look at six and fourteen.
You may have to get on with a tech line and they may have to walk you through pin by pin testing. But why this doesn't have communication on the
on the data network is got to be the reason why this car doesn't start, because that will hold up the PCM that will put this car in theft, the turrent and everything else that you're experiencing.
All right, kitto, sounds good?
You do that you need more? You know where to
find me?
Yes, sir, I appreciate it alrightly.
Anytime, Pal, anytime, Rod and Any and the car doctor eight five five five six nine nine zero zero. We're
back right after this. Yeah, there we go all over
along with Rocky gms. You're calling over forty thousand break
fluid containers. I want to get this out before we
get out of here this week, General Motors, you're calling more than forty thousand containers of ac Delco GM Dot three breake fluid. They're calling tens of thousands containers after
federal regulators found certain batches may not meet acquired safety standards and could contain visible sediment that may affect breaking performance.
The recall involved more than forty thousand units of ac DELCOGMW dot three break fluid distributed in the United States, according to a notice published on National Highway Traffic Safety, GM decided in April to proceed with a non compliance recall after completing its internal review and confirming federal testament results. So,
if you've got some ac Delco break fluid sitting on the shelf and you've got your doubts, get it down to your local GM store. I guess or you know
you can check the part numbers the recall. If you
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on a date code, so you can find that out through GM and just be aware of it. Nothing worse
than counting on a good break fluid. So, by the way,
it's speaking of accounting on I want to count on you, guys.
I do count on you guys, and I appreciate you guys.
I haven't given you the podcast numbers. Podcast numbers are
up once again. We had a three and a half
almost four percent climbing podcast numbers this week, so obviously you guys are loving the social media. We're gonna continue
to do it next week. We've got some really great
topics coming up, one of which we're gonna be talking about batteries and how to pick one till then till the next time. I'm Ronn and Andy and the Car
Doctor reminding you good mechanics aren't expensive, they're priceless.
See ya, he's the car Doctor.
Carr advice to rite
About this episode
Fuel trims, EVAP readiness, and even thermostat or wheel-speed-sensor issues can cause real drivability and safety effects without triggering a check engine light. The show also breaks down misfire diagnostics—how “ghost misfires” and code types like P0300 vs cylinder-specific codes can mislead, and how timing (idle vs off-idle) points toward fuel trim or valve-train problems. Road-trip prep covers battery type matching and responding to long-running warning lights. Later, CANbus/no-communication cases get traced with scan tools, OBD-II checks, and module isolation.
Ron Ananian, The Car Doctor, opens the hour continuing the conversation about fuel economy and why modern vehicles can lose efficiency long before a check engine light ever comes on. With Memorial Day and summer travel season approaching, Ron explains how issues with fuel trims, EVAP monitors, thermostats, wheel speed sensors, batteries, and basic maintenance can quietly affect fuel mileage and vehicle reliability. He also reminds listeners why now is the time to inspect tire pressure, batteries, fluid levels, and wiper blades before getting stranded roadside during holiday travel.
Later in the hour, Ron helps a Toyota Tacoma owner work through an intermittent misfire problem by explaining how modern computers actually detect misfires and why live scan tool data is critical for proper diagnosis. Another caller describes a rough-running Chevy Sonic with a long-ignored check engine light, leading to a conversation about how vehicles adapt around existing faults and why delayed repairs can create additional hidden problems. Ron also helps a repair shop owner diagnose a difficult Chevy Traverse no-start condition involving CAN bus communication faults, module diagnostics, and theft deterrent issues in modern vehicles.
Ron wraps up the hour with a warning about a General Motors brake fluid recall involving certain AC Delco DOT 3 brake fluid products and reminds listeners to check affected part numbers before summer driving season gets underway.
