221: Start/Stall Cadillac CTS Diagnosis

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Hey, what's going on?

Automotive World.

Welcome to another episode of the Automotive Diagnostic Podcast.

My name is Sean Tipping.

I'll be your host once again for today's episode.

Thank you so much for joining me Today on the show.

I'm going to share a case study on a 2013 Cadillac CTS with a 3.6-liter

engine.

This is a vehicle I was called into for a start install condition.

The shop originally thought this was an anatheft issue, and understandably so, and they would say exactly what it did, where it would start up every time that you crank the engine and it would run real briefly and then it would stall, and this was fairly consistent.

Although they said sometimes they could get this thing to run for a while, it always eventually went back to this state, so slightly intermittent.

But they're like stay here for 10 minutes.

If it starts and it will stop starting, it will do the start stall thing.

They don't have any codes to go off of, and they looked into the anatheft key portion of it and then, after looking at the vehicle, they said they don't really believe that it is a theft-related issue, although they're not 100% sure, which is why they wanted us to come out and look at it.

There's nothing pointing to it being in a theft state, besides the fact that it does the start stall.

Okay, cool.

So I went out and I checked it out and actually I swung out to this shop as the last stop the end of the day, the other day, and so I just wanted to see if I could get a feel for what was going on with this thing.

Duplicate the issue pretty easy.

It was doing it right away when I was there.

This is a push button start or what?

No, I shouldn't say it's a push button.

It's actually like a turn knob style smart key.

So you actually have a knob on the steering column that would simulate turning a keyblade, but it's a smart key setup.

That was kind of GM's transition to go from bladed key to a smart key setup.

Anyways, that doesn't really matter, although I am curious about the keys in the theft system to see, is this some sort of anatheft system?

And there's so many different variations of Even in one vehicle line like GM, so many different variations of the anti theft systems, depending on what vehicle you're working on.

Sometimes I don't know what the anti theft system will do to a vehicle right off the top of my head.

You know there's some vehicles where it won't crank at all if it's in an anti theft state.

And then there's some vehicles that will do this start stall, where it runs briefly and then the PCM recognizes okay, I didn't get the key release password or the handshake from whatever module and then it kills the injectors after, you know, a couple seconds of running.

So anyways, I don't know for sure if this, how this vehicle would even react if it is in a theft state.

But I am able to duplicate what they're talking about and it kind of starts stalls.

Now I don't see the theft light on the dash, and that's one of the big things I'm looking at right away before I even scan.

It is the little lock symbol.

It's yellow on this one on a lot of GMs.

Is that present on the dash when this is happening and it's not now?

That doesn't necessarily mean that it has nothing to do with An anti theft, but if I see that I know that's what I'm chasing.

Okay, so cool.

Let's do a vehicle scan and see what we've got going on.

Maybe some codes will point us to what's happening with this vehicle.

So there's a couple random codes in different modules that I don't think have anything to do with this issue.

The one module I am looking at specifically, though, is the engine control module, the ECM.

Right, because whatever is happening with this engine, whether it be anti theft related or not, the ECM is definitely in control of what's happening, and it's the module that I really want to focus on.

Of course, I'll look at things like the anti theft module, the body control module, other players involved and see what codes are in those, and I actually didn't see any codes in any of the theft related modules, but in the ECM I had one code and in the moment when I saw this code I didn't really think that it had anything to do with my issue.

So this was a P0617 starter relay control circuit, voltage high, and that was the only code that I had in this module Was for this starter relay.

Okay, so I'll document it right.

I do my pre scan and I save it as a report.

So I have all the codes.

But I didn't really think of it much in the moment because that didn't.

It is starting right.

The starter cranks every time I hit the key.

Engine turns over.

It starts a lot of the time and then it'll stall.

But code wise I don't see anything.

And anti theft wise I don't see anything.

And I actually went into the data pids of the ECM to look at the anti theft data pids to see Is it happy with the Security data that it's getting from the rest of the vehicle and it appeared to be right.

You can look at vehicle enable status, you can look at the fuel Um theft related fuel status and everything appeared to be good.

So I can kind of roll that out.

At this point it doesn't seem to be an anti theft issue but it is definitely a problem.

All right, so where do we go from here?

Um, one of the things I tried doing right away was, when the vehicle started, I'm gonna hit the accelerator, and I'm pretty sure the shop already did this too.

But what I'm trying to determine with this is this some sort of drivability issue where maybe I'm not getting enough air into the engine, or something like that, or even Just a scenario where I need to move more air and fuel through the engine and this thing's gonna pick up.

And what I'm listening for is to see does this change at all?

Does does this affect the way that the vehicle is starting or installing?

And again, it can kind of put my mind in the right place of okay, this is what I need to look for, or I can rule this sort of thing out.

So what I ended up experiencing and hearing as I was doing this Was it didn't change anything as far as the amount of time that the vehicle would start, run and stall, but I could actually hear the throttle opening when I did this, because when I had the throttle Pretty much all the way open, I didn't do a full, clear flood, but pretty much all the way open, and I was listening.

I had the hood open and the window down.

I'm listening.

You can actually hear the engine running or you can hear the pistons pumping through the open throttle and the air intake, and at least what that signified to me is the throttle is opening and I'm getting air into this engine.

Now it's still not running, it's still stalling basically at the same point.

Me giving a gas does not affect this at all.

So some of the other basic things I'm going to look at here.

Of course I'll pull up some data pins and just go through the ones that we always want to check when we have a vehicle that's not going to start.

I'm going to look at all my temp sensors, particularly air temp and coolant temp, and those are right in line.

I want to look at my mass airflow sensor and see is that registering something as I'm cranking?

I don't know exactly what a good value is on this thing, but I want to see it go up and show airflow.

Of course I don't want it to go too crazy.

I've had mass airflow sensors that will over read and cause an issue, but I want to see is this thing registering?

It was again, I don't know for sure what a good value is, but it seemed to be reading about 2 to 3 grams as I was cranking.

So it's a registering airflow going into the engine.

I'm going to look at crank RPM and see is the engine speed registering and all the way to a stop right?

Is this something where we're dropping out, losing a crank signal or something like that?

I didn't see any issues via the scan tool.

There RPM appeared to follow exactly what the engine was doing.

I also want to look at fuel pressure.

This is a GDI engine and you can actually look at both the low and the high side fuel pressures on this thing right through the scan tool, so that's super easy to verify.

Hey, do we actually have fuel pressure?

Because a start stall issue can very often be caused by a fuel pressure issue.

Right, let's say we adjust enough fuel pressure in there so that it sprays a little bit of fuel into the engine and it's not able to maintain anything after that and so the engine quickly stalls.

That could definitely be the case here.

Shop did say they check fuel pressure actually, but I always have to verify this stuff for myself and both the low side I think it was around 70 psi somewhere in that neighborhood and then the high side, which after cranking and starting installing I was up to 1500 psi, 1700 psi on the high side of this GDI engine.

So we definitely have enough fuel pressure for this thing to start.

And I have found actually on these three sixes this is on the Icadias and the traverses and stuff I've dealt a lot with no starts in these things.

They actually don't even need high pressure fuel to start.

Now to run is a different case.

But these things will start and idle on low side fuel pressure and I can tell you that because a lot of people will leave the follower out for the high pressure fuel pump when they do an engine right, they'll bolt the high pressure fuel pump on to that, the back of the cylinder head, there where it rides on the camshaft.

But there's a little lifter or a follower that goes between the pump and the lobes on the camshaft and if you don't put that in, no motion is transferred from the cam to the high pressure pump.

You don't build up any high side fuel pressure, it's just running off low but it will run not great and you can accelerate and there'll be codes, but it will run off of that and I've seen that multiple times where these things will start and run off low side pressure Either way.

It doesn't really apply to this.

I have adequate fuel pressure for this on both sides of it, so it doesn't appear to be a fuel pressure issue.

Now, while I'm on the topic of fuel and I need to start doing some checks here to see what's going on one of the things that can cause a start stall scenario and in some cases it won't run at all is contaminated fuel or even fuel that's E85 in a vehicle that's not meant for it.

Right, and that was a no start because of E85, and that doesn't happen in every vehicle.

Obviously, some vehicles are meant for it and can adapt.

Some vehicles are just going to run lean when they have E85 in it and they're not meant for it, but occasionally they've run into them where it won't even start.

Now, a lot of the times that happens in the wintertime when it's really cold out, and the day when I was at this vehicle it was actually about 90 degrees and they had the same parked in the sun.

It was definitely warm enough.

But I've also seen just contaminated fuel cause issues where you have water in the fuel or just you got a bad batch of gas and it will just briefly start and then it stalls.

And so again once while I'm on the topic of fuel, I always like to get a fuel sample.

I just had a RAM the other day.

Actually that was a start-stall scenario and then eventually it would just do a real long extended crank and I got a fuel sample from it.

It kind of looked like gas until I added some water to it and it turned like a milky substance that wouldn't separate and I actually think it was mostly water and a little bit of gas in that RAM.

But I really stressed getting a fuel sample for stuff.

It's such an easy test and it's often overlooked by technicians is to actually look at the gas and see is this actually gas?

Is there anything else in here?

So I have a gauge, and this one actually has a straighter valve on the back of the engine.

So again, a very simple test to do, and then I don't have to think about that anymore.

So I got a fuel sample from this thing.

It's normal pump gas and actually in pretty good shape, so I can kind of move past the fuel supply.

Now we still don't know if it's actually being injected into the engine, and that is probably going to be one of my next things I want to look at here.

Is the injector pulse actually dropping out?

Is that why this is stalling, or are we dealing with something else here?

Now I had, along the way, cleared the codes out of this thing after my initial scan and after messing around with it, and I did notice, just by going through this with the scan tool and attempting to start it, attempting to get it going, that the P0617 that I had mentioned, the high voltage on the starter, really control circuit actually popped back up more than once.

So I cleared this thing out and it came back a couple different times and again I really wasn't thinking that this was related to my problem until it started to keep.

It kept coming back and I'm like, hmm, I wonder if this does have anything to do with it.

And so now I'm kind of deciding do I want to start scoping injectors or do I want to go after this code and see if it has anything to do with my problem?

So the next thing I want to do is determine as far as injector pulse and coil pulse goes, are these continuing all the way to an engine stop, or is the computer stopping its pulse of the injectors and that's why the engine stalling.

I kind of want to get a feel for what's going on here, and so the next step is I want to grab a scope and I'm just going to pop it around an amp clamp around one of the wires going to the injectors.

Now the injectors are under the intake on this thing, but on these three sixes, if you look on the backside of the engine and this engine on this Cadillac is conventionally mounted right to the front of the engines, at the front of the car, but you can still get to these.

If it's a Traverse or an Acadia, it'll be over on the driver's side, but backside of the engine there's two plugs and they have all the injector circuits there, and just pick one, put your amp clamp around it and I'm just looking to see is the injector being pulsed?

So I put that around, I got my scope up, I'm looking at this and I crank it.

What I found was, when the engine would stall, the injector pulse was stopping, like it was completely dropping out, the computer was no longer pulsing that injector and of course the engine stalls at that point.

And so now this, I guess could be considered a commanded stop of the engine.

Obviously I don't think it's intentional by the computer, but the computer is dropping out the signal and I actually didn't even go to the coils, didn't really matter at this point, I'm just looking at it as okay.

Why is the computer stopping the injector pulse?

What is it missing?

And of course I go back to crank and cam.

Does that have something to do with it?

I don't have any codes and I went back and I checked my codes again just to be sure.

What I did notice was my P0617 starter relay control circuit voltage code was back and I cleared that out after I did my initial report.

That thing popped back up.

But I have no cam crank sensor codes.

I look at the data pins again.

I look at the cam data Pids.

Nothing seems out of line, out of time.

There doesn't seem to be any issues.

But I'm kind of suspicious of this starter code that keeps popping back up, cause I cleared it and it popped right back up again and I'm just wondering does this have anything to do with the problem that I'm having?

Cause I don't see anything obvious within the scan tool that would be causing the ECM to drop out.

I'm not losing communication with it or anything like that.

It's not setting any anti-theft codes.

All of my data pins appear to be normal, but I have this code, and so in a situation like this, you have to make a decision.

Am I going to follow this code Right, cause it could be a complete waste of time and have nothing to do with my problem, but at the moment where I'm at, it's the only thing I have to go with no-transcript.

Now, looking back on this hindsight, I think there's maybe a data pad that I could have spotted and might have pointed me towards the fix.

But I didn't see that, and so I was going with what I had, and I Determined by looking at the diagram that this is a pretty simple circuit for the starter relay.

I'm just gonna look into it and see does this have anything to do with my problem?

And I am confident that I can quickly assess it and Then at that point make a call whether I have anything to do if it's related to the issue.

Okay, so again, the 617 code is the computer saying that there is Voltage on the control circuit of the starter relay, when it doesn't want voltage to be there.

So this starter relay, which is in an under hood fuse box, is Powered up on the control side by the ECM.

When the engine wants to crank and it does work the engine cranks every single time.

And then on the other side of that control for that relay, there's a ground that goes somewhere on the vehicle.

So it's always grounded and the computer supplies voltage and what the code is indicating is hey, there's voltage here, when we don't want voltage here, okay.

So this should be simple enough to determine.

I go to the starter relay and you can actually pull up data pins if you go to the electrical portion of the data pins on the scan tool For the ECM and you can look at the different circuit tests.

There's an open, there's a short, I think there's a third one too, but there's Pids that indicate the circuit status for this relay, which is pretty helpful.

And when I have the relay in, it basically says yes, there's a short to voltage on here.

Okay, and that's what the code is indicating too.

So this is a hard fault.

It's happening right now.

Now I pull the relay out and it goes to open, but the short to voltage goes away.

So I affected something.

All right, so let's look at this and see.

Now I go on the control side of this relay with my test light and I just want to see does this light up?

Is there voltage there?

And there's not.

And I wouldn't expect there to be.

And I guess that makes sense, because if there was and there's full ground on the other side that relay, it all is beyond.

I guess it depends on how much voltage, of course, but let's check the ground side of it too and see what's going on there.

I've grounded my test light and I touch it to the ground connector for this relay and it lights up.

It's dim but it lights up.

But what that means is there is voltage on the ground side of the relay.

All right, now, a lot of us are familiar with.

If you see voltage on the ground side of a circuit, it means you have more resistance Before that circuit actually gets to ground.

That's what that means.

Now I pulled the relay out, so you might say, well, it's an open circuit.

That doesn't make much sense.

But I'll try to explain this as we go.

But I think I found my problem and If I plug the relay back in it goes to short, to voltage again.

So it is seeing the voltage that's on the ground side of that relay through the relay control coil and then onto that control circuit All the way to the ECM and when the starters not being activated, it's an open circuit at the ECM side and so it's just measuring the voltage.

The same voltage I measured with a test light all the way to that circuit at the ECM and saying, hey, I'm not commanding voltage here, but it is there and Now.

That also makes sense as to why the relay is not being activated all the time, because although there is voltage on the control side, there's also voltage on the ground side.

The coil is not actually going to be activated here, but that's why this code setting.

Okay, now, I still haven't determined if this has anything to do with my problem, but it's something right.

I haven't really found anything to track so far, but I found this and I have a feeling I could probably figure out where this is coming from.

And right, my head immediately went to okay, we have resistance to ground, so let's figure out where this thing Gets its ground from, and that's easy and easy enough to find out with a diagram.

It's G104, which is located on the radiator support on the passenger side, on the outer portion of the support.

It's just bolted there.

Now, when I looked up the ground distribution on this thing, some things started to add up a little bit.

This ground provides this G104 provides grounds to multiple circuits and One of them being the starter control relay, another one of them being the ignition main relay.

And we also have a few other things here the right front headlight and high beam and high beam relay.

So I wanted to try something here, just to see could I affect this circuit at all.

And what I did was I put my test light on the ground side of this relay, the starter relay, with the starter relay out, and it, like I said, it was dimly lit.

I went into the vehicle and I flipped the headlights to Brights, because the headlights were on when the key was on in this one.

But I flipped it to brights.

Watching my test light, it got brighter, okay, and so now I know for sure I've got a ground issue.

And I've got a ground issue where it's having trouble passing the current through.

Now I'm demanding more current With the high beams and the high beam relay coming on that, wherever this Resistance is before it gets to ground, it's struggling to get all the current through there right, and so more of a drop at the point of resistance.

And so we're seeing more voltage At the point of where my test light is and remember my test lights grounded.

And so I'm measuring voltage on the ground side here.

Now that control side of that circuit is connected to a bunch of other ground circuits at a splice and so the voltage that we're seeing is passing it.

It's originating from other circuits and the full drop is not occurring across across those loads and so it's seen on the ground side before it gets to the final load, if you will, which is my resistance to ground.

So hopefully that makes sense in your head.

But if you ever see voltage on the ground side of the circuit, guess what?

You've got more resistance before You're actually at full ground and you just need to find it.

Now, what I tried doing here I was just messing around, because this ground was kind of buried.

I couldn't see it right away and I actually wasn't even a hundred percent sure where it was.

The location diagram Wasn't real specific.

I had an idea, but this thing's pretty packed in there and I couldn't see.

I just wanted to kind of mess around with this.

Well, what I found out is if I turned the headlights off right, so obviously the high beams are off, but I turned the headlights fully to the off position, I could actually start this thing up and it would continue to run and I had to put the starter relay back in.

But I got this thing running and it would actually idle, and they did say everyone.

So I was thinking idle for a little while, but it was always go back to this state.

Now I'll put a video in the Facebook group as Soon.

As I turn the headlights on and turn the brights on, the car would stall.

And I could do that over and over again Turn the headlights off, it would start up, it would run.

Turn the headlights on, hit the brights, engine would stall.

It was kind of funny.

But what I'm doing there is this ground point.

Wherever this resistance is, I'm demanding more current through and we're losing the ground to those circuits.

And what, in again in hindsight, was happening was the ground for the ignition main relay was failing and that Feed to the ECM Dropping out is what caused it to stop pulsing the injectors Right.

So these things, this is related.

This is the cause of my problem.

Now I just have to find it had to take the fuse box out in a big bracket and Right behind the washer reservoir you can find ground 104 After getting into it in this corner of the vehicle.

You could tell at one point in this vehicle's life Although it looks like it was a while ago, based on some rust, it had been in some sort of collision and that right front of that vehicle had been reconstructed to a point.

Well, when they put ground 104 back on, they did not completely tighten the 10 millimeter bolt that holds it to the radiator support.

You could grab that and you could wiggle it around and you can hear relays clicking and stuff with the key On.

So it was as simple as tightening a bolt down, cleaning it up a little bit, I suppose.

But tightening a bolt down put it all back together and you're good to go.

But I thought that one is pretty interesting and One of the points that I want to bring up there is never completely ignore a code.

You know I say a lot on here is I see some codes that are unrelated to my problem, or at least that's what I think you always want to keep in mind that hey, if I have a recurring code in the module that's having an issue.

It could have something to do with it and I may want to rule that out, especially if I don't have any other leads.

That's what I did on this.

One is like hey, I have a problem, I'm gonna follow it, and it ended up leading me to my conclusion Because that's the only thing I had to follow.

Now, sometimes that's not true.

Sometimes you can go down a rabbit hole, you can waste some time and you know the, the gut call in the moment just kind of comes from experience of is this something I should be chasing or not?

And I've wasted a lot of time chasing the things that wasn't related.

But sometimes you got to go for it, especially if it's the only thing you have.

So I want to share that.

That was pretty interesting.

Check out the Facebook group for the video.

It's pretty interesting.

The the engine stalling every time you hit the brights.

But that's all I got for you today.

Thanks for listening.

Really appreciate it.

Let's get out there.

Suffix in the world.

One card a time.

Cadillac Cts

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