0:00
/
0:00
Prius Smart Key Problems & F-150 Crank No start
Prius Smart Key Problems & F-150 Crank No start
0:00
0:00
0:00
0:00
About this episode
Two intriguing diagnostic cases are explored: a 2011 Toyota Prius with non-functioning smart key and remote entry systems due to a missing 'short pin' fuse affecting the certification ECU, and a 2015 Ford F-150 crank-no-start issue caused by reversed wiring on the crankshaft position sensor. The Prius problem highlights the complexity of Toyota's smart key system and the importance of power feeds to the certification ECU. The F-150 case emphasizes detailed waveform analysis revealing the inverted sensor signal preventing spark, despite proper fuel injection and timing. Both cases showcase deep diagnostic techniques and problem-solving in modern vehicle electronics.
Topics:
toyota prius smart key system
certification ecu power issues
short pin fuse
ford f-150 crank no start
crankshaft position sensor wiring
waveform analysis
coil on plug ignition
diagnostic scan tool data
vehicle security systems
fuel injection vs spark issues
This week on the show I have 2 case studies. A 2011 Toyota Prius that doesn't seem to have any smart key functions & 2015 Ford F-150 that is a crank, no spark, no start.
Website- https://autodiagpodcast.com
Facebook Group- https://www.facebook.com/groups/223994012068320
Email- [email protected]
Filter:
|
Technical
Too Afraid to Ask
Car
Toyota Prius
"... week. The first one is going to be a 2011 Toyota Prius in which the smart key functions and the RK remot..."
Car
Ford F150
"The first one is going to be a 2011 Toyota Prius in which the smart key functions and the RK remote keyless entry functions do not work, but you are able to key up vehicle and get it started eventually. The second vehicle is a 2015 Ford F-150 that is a crank no start, so I'll get into both of these. I thought they both had some interesting solutions."
Select text to request an explanation
Welcome to the Automotive Diagnostic Podcast.
We're going to explore ways to sharpen our diagnostic skills, find learning resources and hear from experts in the automotive field.
Hey, what's going on?
Welcome to another episode of the Automotive Diagnostic Podcast.
My name is Sean Tipping and I'll be your host for this week's episode.
Thank you for joining me.
I have got two quick but very interesting case studies for you this week.
The first one is going to be a 2011 Toyota Prius in which the smart key functions and the RK remote keyless entry functions do not work, but you are able to key up vehicle and get it started eventually.
The second vehicle is a 2015 Ford F-150 that is a crank no start, so I'll get into both of these.
I thought they both had some interesting solutions.
Hopefully you'll find that as well.
Let's start off with the Prius.
Again, this is a 2011 Toyota Prius with the smart key system, which I guess.
I've never seen a Prius without a smart key system, so I think they all have it.
Somebody can correct me on that if I am wrong, but this is actually a technician at a shop that I go to.
I don't know one of his friends' cars.
He was trying to fix it for him or something like that.
He reached his limit on what he could figure out with the smart key system.
Now a little bit of history on this vehicle.
It had the catalytic converter stolen out of it, apparently, and they hacksawed this thing out of there which has been just rampant up here and, i think, in a lot of places all over the country recently, and they fixed all that stuff.
The O2 sensor wiring got cut, but they fixed that.
And he did mention the owner of the vehicle had attempted some repairs after this themselves, which is where I think the problem actually came from.
But this technician got involved as well on replacement of parts.
But anyways, after the vehicle was repaired, or as much as they were able to, the smart key functions no longer work for the vehicle.
So the button on the handle that you press and if you have the key in close proximity it'll unlock or lock the doors, and then you hop in and you press the start button should key up the vehicle.
None of that works.
You can hit the lock and the unlock buttons on the actual fob and those Toyota smart keys have a little red LED, which there's more to checking than just the little red LED, but at least you can say hey, has the battery got some power to it or not?
That was flashing, so it looked like the key was doing something, but no response from the car.
Now if you were to take the smart key and push the smart key up to the actual start button so you're pushing the start button with the smart key eventually this thing would key up and it would start, although it wasn't nearly as fast as a Toyota Prius normally would key up.
You have to hold it there for close to 10 seconds.
That reminded me of a GM.
When you're just trying to do the key up function, you're not trying to start it.
It took a while and I wasn't sure if that was normal or not.
Even with, let's say, you had a key with a low battery, is that normal?
I'm not sure.
I didn't know right off the top of my head, but anyways, you wanted me to look at this.
So I get into the vehicle and I did find that everything he was telling me was correct.
So of course I'm going to start with a full system scan and see what we got.
So there was a number of codes in this that I didn't really feel had anything to do with the smart key functions.
But the one module that is definitely related to the system is the smart key ECU, or also called the certification ECU, and you'll find with these Toyota smart systems they can have two different names for the same component And it's, in my opinion, very complex system just to begin with and then you give things two different names and it makes it even worse.
But anyways, the smart key ECU, or the certification ECU, does have communication codes in it referencing other modules like the ECM and the main body ECU.
I believe there's one other one That was the one thing that stood out to me on my code scan that said okay, hey, something's going on, you know, with this particular vehicle.
The weird thing was was those codes were all history.
So I would clear those out and if the vehicle was running, those codes would not come back.
But if I were to cycle the ignition, turn it off, do the wait to get it to power up and then eventually get it started, those key, those codes would come back, but they would be history again.
So it was kind of strange.
I didn't really understand what was going on there, but I did notice that those codes were in there.
So I mean to check things over and out.
The other thing I wanted to do right away was just to see, okay, is the key actually outputting a signal?
and Then, is the car trying to reach out to the key right?
even though The setup on these Toyota smart key systems are it's fairly complex, the same basics apply as far as the keys got to put out a signal to the car.
And if you were to either touch the handle, the button on the handle, or the Button the ignition, the car should reach out to the key right.
And yeah, there's a lot of stuff behind the scenes happening to make all that work, especially the car reaching out to the key.
But I should be able to measure that.
And I've mentioned the tool before.
It's the diagnostic box Keyless or proximity key tester.
It's awesome, it's battery powered, but it's fantastic for quick checks on these types of systems Because you can check the output of the key.
I mean, and there's a lot of tools that do this, i mean key tool max TPM s tools, all kinds of things will check the.
If you press the button on the fob, is it sending out a signal and what frequency is it?
Right, is the right frequency for the car?
And this didn't look like a new key.
Also, i mean it doesn't mean it belongs to the vehicle.
Well, no, i should back up there.
It does belong the vehicle, because eventually you can get this thing started.
But anyways, the wrong frequency really wasn't on my mind.
But of course I want to check for that.
I want to make sure that the key is correct for the vehicle.
So, anyways, i'm using that proximity key tester and First off, i just hit the buttons unlock and lock on the fob.
I get a signal out of it, so it's outputting an RF signal to the vehicle to say, hey, lock or unlock.
The car is obviously not responding.
Okay now second thing is is the car reaching out to the key?
So I hop in cars off, i have the key in my hand and I reach up with my other hand and I press the button.
At that point, once you press the start button, the car should be triggered to reach out with antennas inside the vehicle on a low-frequency Signal to hit that key and then the key is then triggered to send an RF signal back to the car.
According to my tester and I tried a couple different places in the vehicle, not just in the driver's seat I put in the passenger seat, i put in the back, because there are multiple antennas and they are short-range.
For anybody that's been in a push button start car, you know how short they are because of the key is just outside of the door frame, generally you won't be able to start the vehicle up, so they're very specific ranges.
So I'll move the key around the vehicle just to see.
Okay, you know, am I picking up a signal anywhere?
and I wasn't.
So Based on what I was seeing with my tester is the car was not responding to the button pressing That I was doing with the key.
Like that signal is going out from the key but the car is not responding and The car does not seem to be sending a signal out to ask hey, okay, he pressed the start button, does this key belong to this vehicle?
That signal is not coming out to trigger the key, to send its information back to the car.
All right, and that That's at least that part of the smart key Operation is pretty standard across most makes and models, if not all.
I'm sure there's exceptions.
I mean, there's some semi smart key setups out there as well, but for the most part smart key Systems are gonna work in that fashion, all right.
So now I have to figure out What's going on and in order to do that, i need to be Familiar with the system operation.
Now, i've been through these Toyota smart key systems before and, like I mentioned, i think the whole, the whole operation is very Complex and I actually I have some info on these systems that was shared with me credit to PJ Walter for helping me out with some information on these.
But the It's a PDF with an operation of the smart key stuff.
It's a 30-step operation in order for the whole smart key system to function and Power up the vehicle, start the vehicle.
There's a lot going on and there's a number of components involved too.
We have that certification, certification ECU or smart key ECU.
What I have found is the name in the service info of the component Does not necessarily match the name of the component in the scan tool, and that's where it gets confusing, because if I'm trying to diagnose the system, i got my scan tool in my hand and I'm reading service info.
The names don't always correlate, so be aware of that.
But We have our certification ECU or smart key ECU.
We have the steering column lock ECU, which you can't communicate directly with the scan tool.
It's only on a LIN bus.
You have the ID code box which, same as the steering lock ECU.
You do not have direct communication with the ID code box via a scan tool.
It's on a LIN bus with the certification ECU, with the steering lock And you have the main body ECU, which I believe was called the power source in the scan tool.
So again, different name there, but I would also just call it a body control module for my own personal preference on lingo.
But Toyota calls it main body ECU or power source control.
I think was the scan tool, and then also the ECM.
But the ECM's not really involved right away.
We go through a lot of other processes in this smart key system before we even reach out to the ECU.
But main body ECU, id code box, steering lock ECU and certification ECU and then the ECM as well.
Okay, so a lot of components right off the bat.
Oh, and you have the key as well, the button on the dash and the antennas that reach out to the key.
So again, a lot going on there, and I've read through this process before, but I saved this PDF that I have because there's so much going on.
There's, if you really get deep into it, which I'm not gonna do here, because, number one, you need a visual and number two, i don't wanna make this episode two hours long There's different codes that you can read as data pins within the scan tool S code, g code, l code to see what part of the system is not functioning or missing or there's an issue with, and that can lead you down different paths as well.
But again, i invite you to actually go through the system description operation I mean it's in service info as well.
It's quite complex.
I think it's overly complex personally, but that's why I have to read up on this one, because I'm like boy, i don't remember all the details on this system right off the top of my head.
I don't deal with these every single day, and so I kind of forget the path that things go.
I actually, the last time I did one of these on a Highlander, i took out a piece of paper and I drew myself a picture to help me understand, like you know, that whole thing where, like, explain it to me, like I'm five, like I have to tell people that sometimes, like, i need this dumb down to a Sean version, and so I drew myself a picture of this system to help me understand as well.
But anyways, i also happened to be talking to PJ this day when I initially went to this car.
The tech had just I was at the shop for another reason And he's like hey, i got this Prius, you want to take a quick look at it?
And so I gave it my initial inspection and I told him let me read up on this and then I'll come back.
I didn't have time that day to dig too far into it anyways.
So I happened to be talking to PJ later that day And I asked him.
I was specifically asking him about hey, if you know the battery in the key is dead, let's, for example and you pressed the key up to that ignition switch the start button.
Should it take like 10 to 15 seconds to power up the dash, or is that normal in that situation?
He's like no, i don't think it is.
I was like, yeah, that didn't seem right to me either.
Even when the key's dead, you should be able to power this thing up and get it going, and you eventually can.
And that was another big part of this.
I didn't dive too far deep into the L code, g code, s code thing, because eventually this key did start the vehicle.
So I would assume that all of the modules that are involved with the security and stuff are happy with the key that we're using.
It's just for some reason the smart key functions aren't working.
But PJ did mention something else to me.
He said I think that the certification ECU is bypassed when you're using it, when you're using the key and pressing the start button.
So what I did later that night is I read through the system description and operation and the flow on how things go, the whole 30 step operation And normally what happens again, you press the start button, that triggers, that goes to the main body ECU or body control module which then over a can network, talks to the certification ECU which is going to trigger the antenna
to reach out to the key.
The key sends its information back to a receiver which goes to the certification ECU And then it communicates with everybody else the steering lock, the ID code box to say, okay, is this the correct key?
And we key up, we start the vehicle.
Right, that's the normal process.
But when you are using the key, let's say the key's battery is dead, which it's not in this case.
But let's say you're using the key in a dead battery state, the certification ECU or smart key ECU is in fact bypassed And it's shown in this diagram that I have here of you're touching the key to the start button.
It has an antenna in it to do a short range communication with the key, just like the old school transponder chip keys.
Same thing, but now that main body ECU basically has the key info and talks with everybody else over a LIN bus ID code box, steering lock ECU and even the certification ECU, but on a LIN bus.
And so this really clued me into.
Okay, i need to focus in on the certification ECU for a couple of reasons.
Now I can talk to it with a scan tool.
I told you I got codes out of it, but it does reset communication codes with every ignition cycle And the only way we can get this vehicle fired up is by seemingly bypassing the module.
And I didn't realize that at first.
But after PJ mentioned that and I read through the operation, i'm like, yeah, this thing gets bypassed when we're holding the key up to the dash.
Plus, i got some communication codes.
Okay, this is where I need to go first, so you can access this thing behind the glove box.
There's a number of components there, but one of those is our certification, ecu.
And so first thing I'm gonna do on this thing especially cause we had some wiring damage underneath I'm just gonna check all my powers and grounds to it.
Maybe we're missing a power, maybe we're missing a ground.
And this is super easy to do on this thing once the glove box is out, just get your diagram.
Boom, boom, boom.
Let's verify all that stuff, get that out of the way before we move forward at all.
So I do that and I am missing a power feed to this module.
So, looking at the diagram, this power feed comes from ECUB fuse in the unheard fuse box.
Okay, easy enough, let's go see.
Maybe we're missing a fuse, maybe it's blown.
I go to the fuse.
The fuse does not have power on either side of it, so that fuse is missing power.
Okay, so I go to my power distribution diagram to see where does ECUB fuse get its power from?
Well, it gets it from something called a short pin, and that's Toyota's name.
It just says short pin.
And I had to look up a diagram, a fuse box, to see where this was and I really wasn't sure exactly what it was.
But in searching for the term short pin, i did find a service bulletin about a short pin which basically says when these things roll off the truck, when they're first delivered, you have to take them out of a transport mode And one of the things that you do for transport mode is moving this short pin into position.
But they also in the TSB say that you can take this short pin out and there's another spot that you can put it in the fuse box and it's like a storage mode for the vehicle.
It must prevent battery drain.
Well, this short pin, which kind of looks like a fuse, but it is specially shaped, it has its own spot right in the middle of the under hood fuse block.
Maybe it's not there, there's nothing there.
And I looked in the other spot where there's like a holder for it.
I don't see it.
I don't see anything in the fuse box that looks like whatever goes in the spot.
Again, i was going to try to put just like a normal fuse in there, just to see what would happen.
But you can't, unless you were to cut the fuse to fit.
You can't just put a fuse in there.
And I think that's on purpose.
But what I did was I just took a jumper wire.
I went across these two pins because one did have power on one side.
The other side was leading to my fuse row And there was a couple of different fuses there, one of those being ECUB, which fed the certification ECU.
So, anyways, i jump across there and then I go and then everything works.
Smart key functions work, rk functions work, everything's normal at this point.
So the short pin fuse was missing and somebody obviously removed it.
I mean, i run into this all the time, all the freaking time, where fuses are gone.
This one was a little different.
I haven't run into the short pin thing.
I'm sure if you work at a Toyota dealership you know all about that But I thought it was pretty interesting the way that it acted Where, basically without that power feed to that certification ECU, it did still did have power.
I could talk to it with a scan tool, but it had some communication issues with other modules.
It must be because it's missing a power feed and it wasn't able to operate the smart key functions.
It wasn't able to maybe trigger the antennas in order to reach out to the key or see that there's an RK, an RF function coming in from the key, like without that power feed, that certification ECU loses all those abilities.
And that's hard to say exactly why, unless you trace the inside of the module, but that's the way that it acted.
So if you run into that on a Toyota Prius and there might be other versions of Toyotas with smart key systems that are the same check to see if the short pin it's this little clear white, looking kind of like a fuse, but right in the middle of the fuse block, just to make sure it's there something to check for.
So anyways, i thought that was interesting.
All right, the next one 2015 Ford F-150.
This was a vehicle that was purchased from an auction by an individual who said that the vehicle would not start for him, or he heard it pop a couple of times or maybe struggle to start, but he wasn't able to get it running.
He attempted some repairs himself.
He replaced all of the camshaft sensors, the crankshaft sensor, all the plugs and all the coils, and I think at that point he gave up and he brought it to a shop, which is the shop that I service.
At the shop they looked at this thing for a little bit, kind of went through the basic checks, you know air, fuel, spark, whatever.
They weren't able to find anything that really stood out as to why this thing wasn't starting.
So calls me in and said, hey, can you come look at this one, at the 5.0
engine?
I don't know if I mentioned that already or not, but hey, can you come look at this thing, see why it's not starting?
Okay, cool.
So come in, take a look, verify.
Yep, it's a crank, no start.
I did notice it was cranking really fast like sounded like low compression to me.
So you know, obviously you got to consider is this like a timing chain issue or mechanical engine issue?
I'll keep that in mind as I'm proceeding forward.
But let's get some tests.
Actually say for sure, yeah, this is your problem.
So scan this thing for codes as well.
I have nothing relevant in this thing at all.
There's no codes that are of any help to me, nothing in the engine control module.
And I cranked it a few times just to see, okay, is something going to reset after I try this thing enough.
And there was nothing.
I also got like nothing as far as a pop or, like you know, sometimes an engine will kind of try to start a little bit.
You'll hear a couple cylinders hitting.
Air was nothing, it was just cranking, and again fast.
But it was just cranking.
Okay, no codes.
Let's take a look at what we've got in the data pins that I can see just from cranking.
You know, try to get as much information from the scan tool before I jump under the hood on this thing And the things I'm going to look at here.
And the guy had told me he replaced sensors, so, okay, where to get the sensors from?
that's usually the story.
I'm going to look at that sort of stuff first and there are cam and crank data pins in the scan tool data for this Ford.
You can look at engine speed.
That was one of the ones that I popped up.
You can look at cam and crank sync and that will actually change during cranking from.
You know, it's no when you're not cranking and the engine's off, and then, if the engine is in time, it's going to say yes.
Look at engine RPM.
That's generally a indicator to me that the crankshaft sensor is doing something.
So I crank this thing over and everything appears to be where it needs to be.
I see engine RPM.
The synchronization pit actually switches to yes.
So I can't say that.
I'm 100% sure that always means that the timing's on, but for me it's a good indicator that, okay, yeah, it's seeing a cam and a crank signal and it likes where they're at in reference to one another.
At least enough to start the engine, maybe, okay.
But what I see in the scan tool data okay, this thing should be starting based off of those signals.
Okay, so I'm going to do my basic checks as well Fuel pressure, and I also check fuel quality on anything, especially if it's from the auction.
But if I'm hooking up a gauge to measure pressure, there was because there was no pressure sensor on this version.
I'm going to do a fuel sample as well.
I've gotten into that habit because I run into so many vehicles that fuel quality is the issue.
So I do both of those things.
Looks great, good fuel, good pressure, all right, so we got that.
And next thing I'm going to check for is actual fuel injection and spark.
Okay, so easy enough.
And I find I do have fuel injection.
It's pulsing injectors as long as you're cranking it, but I do not have spark out of this vehicle.
Now I have powered the coils.
These are coilover plug.
There's eight coils for the engine And it gets a constant power feed with the key on and the computer is going to directly ground the coil, right?
So these aren't the style where there's a transistor built into the top of the coil.
This is just a coil and it is wired straight up to the PCM And the PCM is going to ground each coil individually.
Well, the PCM is not doing that.
Now, i did not test all eight coils, but I tested the fuel injection, but I tested the front two, so that would be cylinder one and cylinder five on this engine, and neither one of those had a grounding from the PCM.
So that was enough for me to say OK, i got to look towards the PCM here, because why would it not be grounding these coils?
So I go to the PCM connector and I test there as well on the coil control circuit, just in case.
Maybe.
We got an open circuit and I verified that the PCM was not doing anything there and I also just double checked to make sure that I had continuity between that point of the PCM and the actual coils.
I did So it's not like a connector issue or something like that that's keeping it from getting the control to the coils.
This just doesn't seem to be grounding the coils, which is weird.
And again, no codes in this thing referencing anything to do with something that would stand out to me as like why are we not sparking on this engine?
And it's not an anti-theft issue.
Spark, generally speaking, doesn't have anything to do with an anti-theft issue.
Now, one thing that can, and that is on my mind now, especially because the engine is cranking fast, is maybe timing.
Okay, so there could be a timing issue.
Now, i'm not thoroughly familiar with this year and engine computer strategy when there's a timing issue.
You know there's a lot of cars where if timing's off by a certain amount, it'll spark cylinder one one time and then it will not do it at all.
Now this vehicle wasn't sparking at all period.
Again, i didn't check every single cylinder, but the two that I checked.
There was nothing, no control at all, but maybe that's the default state if the timing's out.
Now the cam sync data pid said yes and there are no timing codes.
But do timing codes set on this one cranking?
Probably not, i would say.
Most vehicles you have to start.
That's not true for all of them.
Most vehicles you have to start if you're going to see some sort of cam crank correlation code.
So this is where having a scope is going to be really helpful.
Again, i heard the engine compression sounds low.
It's cranking fast, not having spark.
Now it's weird that it has fuel injection but not having spark.
I got to look at my timing.
I got to make sure cam crank stuff lines up.
So you know I'm using my four channel Pico for this and you know usually I'll use my Uscope for most stuff that I scope.
But cam crank is definitely an area where the Pico shines because you can do multiple channels, obviously, but you can also get really good detail and manipulate it very easily where that part of things is where the Uscope is a little bit less useful.
Not that you can't figure some stuff out, i mean, you can't do multiple channels.
But for the detail side of things and Pico is just where it's at And if you combine that with a touchscreen on a laptop man, that is the bee's knees.
I like that The touchscreen and the Pico you can really manipulate waveforms easily.
So get my cam crank.
I have to do one side of the engine at a time because there's four cam sensors and one crank sensor, but the known goods that I found were set up that way as well, so this will make for an easy comparison.
Okay, now I wanted to thank somebody on Facebook here, ray Yergo, and I hope I'm saying your name correctly.
I don't know how it's pronounced for sure But if you're in these Facebook groups you've done some known good waveform stuff.
You've probably seen this guy's name.
He's on Diagnostic Network too and he seems to have every known good waveform that you could ever want.
So thank you, ray, used your known good waveform for 16F150.
And of course, we want to be careful.
We're using a different year but had the same engine, so I was comfortable using this one in order to line up to see, hey, is everything in time or are we out of time?
And that's what's causing my problem.
Well, long story short here.
I'm pretty meticulous about lining this stuff up and go back and forth and, okay, does this look right?
It really comes down to do these look the same or not, but I go back and forth between these two waveforms and make sure that, yes, everything is lined up where it's supposed to be.
All my cams, in reference to my crankshaft sensor, are correct, right on the money.
So I'm starting to think why isn't this thing sparking then This is really strange.
I mean, maybe it's a bad PCM, maybe I need to start checking powers and grounds to my PCM, maybe it's missing one, and I was going to do that.
I was actually thinking about pulling up a diagram for powers and grounds to my PCM because I don't know what else would cause no spark control.
But we do have fuel injection pulse And I was thinking about that too.
I'm like boy, this thing's spraying fuel every time it's being cranked over.
The injectors are actually firing.
I was like this thing might just be flooded.
They're like the cylinder walls wash down.
That's why it's cranking so fast.
And I'm saying this now that I see that the physical timing is intact, that it's where it needs to be, that that's not causing a compression issue.
But I was like, well, maybe cylinder walls are just washed down from these injectors firing and there's never any spark.
So we just have a big buildup of fuel in the cylinders.
And back to my question why wouldn't not be sparking at all?
I think this is a little bit of dumb luck that I just happened to notice this.
I don't want to come off as like I have this super awesome attention detail and I can pick out things like nobody else can.
That's not what this is.
I just, i just happened to notice this as I was bouncing back and forth to the two waveforms, the known good and mine off of the vehicle.
Now, of course, i'm lining up.
My main focus is I'm lining up the camshaft pulses to the crankshaft waveform.
So I'm bouncing back and forth, trying to line up and really focused on where the camshaft pulses intersect with the teeth on the crankshaft.
I'm counting crankshaft teeth and making sure, okay, bank one intakes right here, bank, you know, two exhaust is right here.
And then making my judgment off of that and with bouncing back and forth, i just happened to notice where the missing tooth is on the crankshaft.
Right, we have a missing tooth, a gap in that crankshaft or a luchter to indicate to the PCM exactly where this thing is in rotation.
Right, it's the trigger to the PCM to say, hey, okay, we've crossed this point.
Now we start counting after this point and it gives it that you know exact reference of where it is in rotation, where the crank is.
It was there, the missing tooth was definitely there.
But it's a inductive sensor, a variable reluctance sensor, meaning it makes its own voltage.
It's two wire.
It's an AC waveform, right?
If you've ever seen one of these.
They're little spikes that bounce up and down and then you have a big one.
At the missing tooth right.
You have one that extends a little bit higher than the rest And I'll put a picture in the Facebook group here so you can see this At the point of the missing tooth on the known good waveform, the voltage drops down as soon as we hit that missing tooth and then it comes back up.
It goes to a positive state before we start hitting the rest of the teeth.
All right, so if you imagine you're looking at a scope and you're reading left to right, like you would, a book, as soon as we hit that first part of the missing tooth, voltage drops and then we rise back up before we finish the missing gap and go back into the teeth.
So it's down.
Up is how this works.
Okay, on mine, it just happened to notice this bouncing back and forth.
On mine the voltage goes up and then down as you're reading left to right, and I looked and I compared back and forth, back and forth, back and forth.
Okay, that's correct, and I wanted to make sure.
I'm like oh, hang on a second, did I do this right?
And again, credit to Ray.
He's detailed enough to tell you what pin he is on on the PCM And so I verified.
I'm like, yep, i'm on the exact same pin as he was, but mine is different.
And I double check.
I got the waveform again just to make sure, like I didn't have my leads flip-flopped or anything like that.
Mine was 100% inverted from what his is.
His goes down up, mine goes up down, okay, and I'm starting to wonder.
I'm like I wonder if that's enough of a difference And I also wonder how that could be happening.
Well, these style of I shouldn't even say style of sensor, i should say forwards version of how they measure a lot of their variable reluctance sensors is what's called a floating ground sensor.
Now, if you're to actually do some scope work with one of these AC generating, you know, variable reluctance sensors, you'll see that there's actually voltage on both sides of the sensor, and that's just the nature of alternating current.
The AC voltage that it produces is it's gonna bounce one Direction or another positive, negative, positive, negative.
Now what we do in a lot of cases I would say most vehicles that use these types of sensors is we ground one side of the sensor and then I'm talking as a PCM we ground one side of the sensor and then We're going to monitor the other side of the sensor, the signal wire, the positive wire And we're looking at voltage there.
And if you're hooked up to the vehicle and you're using vehicle ground as the reference for your scope, you only see a Signal on one side of the sensor and then, if you hook to the ground, you don't see anything because your scope's reference to ground and you've got the lead on ground.
You're not going to measure anything.
But in reality There is voltage there, voltage being produced by the sensor.
But we have to think about this in.
The only way we're measuring voltage is by comparing it to something else.
And if we've grounded vehicle ground Remember vehicle ground if we've grounded one side of the sensor, we're not going to be able to see anything of the scope.
Right, and it doesn't matter.
In that case Computer's not even looking for that.
That would be a non floating ground sensor.
Now Ford uses a floating ground sensor where they don't ground either side of the sensor and You can measure voltage on both sides of the sensor, and that's been true for a long time.
They've done that a lot of vehicles with their crank sensors, and there's others too, i know.
So there's some Hyundai Kia stuff that does that as well.
So if you see voltage on both sides of a crank sensor, on one vehicle and not on another one, don't be surprised.
That can definitely happen and, for whatever reason, ford has chosen to do this with a lot of their stuff.
So I get to thinking, okay, well, how could it be inverted?
Well, what if the wires were backwards?
or maybe the sensor itself somehow Backwards inverted, i don't know.
Okay, well, let's get down to this crank sensor which is on the passenger side, behind the rear head, going into, you know, the bell housing area, just to see what's going on, get a visual on this thing.
You know, i knew this sensor was replaced and so it was pretty easy to access.
We pull a little panel away.
Well, once we get in there, it was very obvious what was going on.
Somebody had done some wiring repair right at the crank sensor and By doing a little bit of work, looking at the pinout for the crank sensor, looking at the diagram, i found that the wires were backwards from where they're supposed to be.
So, okay, well, let's, this is easy enough to try out.
So we cut the wires, we just flip-flopped them real quick and as soon as I did that, this thing pop, pop, pop, pop As I was cranking it and then eventually it did start and there's a bunch of smoke and everything And it actually ran halfway decent after a few seconds.
But I told him me, hey, you got to change oil on this thing before you run it for too long.
You got a bunch of fuel in there, but it started and ran and so that was it.
The fact that Even though the missing tooth was there, it was inverted was enough to throw off the PCM.
And I had to look at a little bit of service information To try to figure out exactly why.
Because it still didn't make you know all the sense in the world that this thing Would fire the injectors, but it wouldn't fire The spark plugs at all or the coils at all.
It just is very strange, and I read up a little bit on service information for this One of the things.
When you're looking at the ignition system for this Ford.
It says that the CKP sensor indicates the crankshaft position and speed by sensing a missing tooth on the pulse wheel mounted to the crankshaft.
The COP integrated electronic condition system uses the CMP sensor to identify the compression stroke of Cylinder one and to synchronize the firing of the individual coils.
Now, the second part here is referencing what we're dealing with.
The PCM uses the CKP crankshaft position sensor To calculate a spark target and then fires the coil pack for the COP to that target shown.
The PCM uses the CMP camshaft position sensor To identify the compression stroke of cylinder one and to synchronize the firing of the individual coils.
The PCM controls the ignition coils after it calculates the spark target.
After it calculates the spark target, right, the COP system fires only one spark plug.
Blah, blah, blah, blah.
There's more stuff there, but that's the key piece of information that made this make sense, right?
So it's using the crankshaft position sensor to fire the coils, it's using it to calculate a spark target and after it calculates the spark target, it fires the coils.
Well, it wasn't able to do this, apparently, when the sensor signal was inverted, right that when the Voltage went the wrong direction, it was not able to see that missing tooth.
And I've seen this with other things, where the voltage moves in the wrong direction.
I think I had a grand caravan with a similar.
It was a Hall effect sensor So it was a little different.
But the voltage would move the wrong way at the missing tooth and although you could see it on the scope and Measuring it compared to another one, it's in the same spot.
But the computer is not seeing it in the same way that we are.
It's seeing, you know, falling and rising edges of the voltage and if that doesn't happen, where it's expecting it to, it's thrown off.
Now the interesting thing was is that it was Showing rpm in the scan tool.
Was it just counting the smaller teeth and giving me that?
was it looking at camshaft revolution?
I don't know how that data pit is determined, necessarily, but it showed me rpm in the scan tool And it was firing the injectors and if you read in the service info, it's using the camshaft sensors to To synchronize the fuel offense.
And so I'm guessing, because it saw a good camshaft Sensor signals and saw something from the crank sensor.
I mean it didn't send any crank sensor codes, so it must have been saying, okay, well, i'm seeing something, i'm still just waiting for that missing gap so I can do my spark target.
But it was firing the injectors which flooded the engine and so that made it sound like it was cranking really fast, but because whoever had done the wiring whenever they did it to this crankshaft sensor got the wires backwards.
Even though signals were getting to the PCM from this crank sensor, it wasn't able to identify that missing gap.
So pretty interesting stuff and an interesting fix for that one.
So hopefully you enjoyed that.
But with that out of the way, let's all get out there, start fixing the world, one car at a time.
Request an explanation for:
2 cars
2 cars featured
Request an Explanation
Heard something you'd like explained? We'll add it to this episode.
Sign in to request explanations for terms you heard.
Want to learn more?
Browse our glossary for plain-English explanations of automotive terms, jargon, and concepts.
Help improve this episode
See something that's not quite right? Our annotations are AI-generated and can sometimes miss the mark. Click the flag icon on any annotation to suggest a correction.
Report incorrect info
Suggest better explanations
Flag missing cars