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2006 chevy
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Discussion Starter · #1 ·
I am relaying I formation from my non-car savy friend that lives three hours away. So you have been warned, lol. I am a mechanic, so there's that.

2002 trailblazer 200,000+ miles, stock.

If she goes out to her rig and the keyfob does not work, the engine will not crank. Keyfob works = engine crank and start.

I have been reading through Chilton and I am unclear if the keyfob has anything to do with the engine cranking. I know that the keyfob talks to the TailGate Module (TGM) and the TGM talks to the rest of the rig. But can the TGM shut down the crank circuit? I know from the Chilton wiring diagram that the crank relay solenoid has fused power to it and that it is ground-side switched by the ECU, so is it possible that the TGM is sending a bad signal to the ECU? Another possibility I have considered is that if the ECU thinks that it's in gear, it won't crank, but would that also disable the keyfob? It is my understanding that if it's in drive, the keyfob won't open the tailgate, but Chilton doesn't mention the door locks if it's in drive.

And then there is the security issue. I don't know if there is any chip or whatever in the key that keeps the car from starting. She mentioned the security light, but we have issues with the cluster. Lights and guages are intermittent and I have talked to a cluster fix shop and they told me that it is a common issue and can usually be fixed. But could something in the cluster be causing this non-cranking issue?

Additional information:

Alternator and battery are fairly new, have tested good and when it cranks, it cranks fast and starts easily.

Grounds can certainly be an issue and it is something that I will do a voltage drop test on when I get up there next week. The rig does have quite a bit of rust, relative to what I'm used to which is zero rust, but its not falling apart - Fred Flintstone - braking rusty. So I need to find as many grounds as possible to check them. I'm hoping Chilton has pictures with circles and arrows, etc. showing the grounds.

The last time that I was up there, it would crank, but not start which turned out to be the fuel pump. I also just got word that after not starting for a day, it now starts, so I am pessimistic that when I get there, it will start.

The rig also has intermittent running issues. She tells me that sometimes she presses in the accelerator pedal and it doesn't have power and maybe it's reving way higher than it should and it isn't shifting. The last time this happened, she shut it off, went into the store and when she came back, it drove normal. So, did a key cycle reset something or did something cool off? I don't know, but I will do a complete scan on it when I get there. Hopefully there is a pile of codes, ponting me in a direction.

Thank yo to anyone that is bored enough to read all of this and understand what I'm asking. It's just odd that if the keyfob doesn't work, it won't crank but if it does work, it will crank.
 

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Going bakwards on your post ....

1. there may be a transmission problem
2. the REP light should be lit if the computer won't allow throttle responce much over 10% or so, with a limited top speed of about 25 MPH.
3. Intermittent running ... if you mean it shuts off sometimes ... COULD he a bad ignition switch ... that's a common problem.
4. Don't hope on those Chilton paperbacks ... they're too generic.
5. Is the SECURITY light on?
7. The fob has ZERO effect on cranking UNLESS the computer is in SECURITY MODE. The horn should be making a lot of noise too. Does the horn even work?
8. The fob will NOT open the tailgate ... it's a manual liftgate, not powered ... after it is unlocked. The dual spring shocks are not sufficiently strong enuff to open it either.
 

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Discussion Starter · #3 ·
First, thank you for your time. Second, I had written a post that the ignition switch was replaced, but didn't hit post reply.

So the ignition switch is brand new. Transmission is about a year and a half old, maybe 20,000 miles, so there could be solenoid issues, but slipping disc's is unlikely. Transmission oil is good, not burnt.

I have never been there when it's not running right. From my understanding, it doesn't die or miss (new coils and plugs recently, because it was missing, so she knows what that's like)

The Chilton I am using is the online version through my library, not the book. I chose to mention Chilton just as a warning that my information may not be 100% reliable. ;)

I know from changing the ignition switch that the horn works. Her neighbors know it works as well. I'm glad that you brought up the security mode because that is the main reason that I came to a Trailblazer specific forum. I know that here, there will be people that know how a trailblazer is supposed to operate, rather than a generic "here's five reasons why your car won't start" article.

Just to make sure, I'm clear on this, if it is in security mode, the horn will also be honking, correct?

What causes it to go into security mode? Incorrect key? Bad keyfob? Something funky on the communication system?

We did open the fob and cleaned it with oven cleaner like I read online. Just kidding, we used isopropyl alcohol. It was rather gooey in there. DISCLAIMER: DO NOT USE OVEN CLEANER TO CLEAN ELECTRONICS. IT WAS A JOKE.

What could be wrong, that would cause it to go into security mode?

What other things will she notice when it's in security mode?

I am reluctant to rely on lights on the instrument cluster because they are so intermittent. It's tough to know if a light is on indicating a problem, or if it's on because the cluster is wacking out at the moment. As I mentioned, she is not car savy, so communication is sometimes difficult.

After all of this, you got me thinking that I need to read the owners manual about the security system. That would probably be the best place to understand what is supposed to be happening. I will see what I can learn there. Is there a repository of things like owners manuals on this site? Like I said, she is three hours away.
 

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Discussion Starter · #5 ·
Well, here's hoping all is well with you PT. she said that the alarm has gone off Randomly in the past but it has never been going off when it won't start.

The fob not working and the engine not cranking happen at the same time, consistently. So the question I am trying to figure out is if it won't crank BECAUSE OF the fob, or is there a different problem that is causing the fob to not work AND it won't crank.

IF, in normal operation, the only time the fob won't work and engine won't crank, the alarm will be going off, then it seems that there is something going on that is causing both to not work? Am I on the right track here, or am I overthinking this?
 

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Discussion Starter · #6 ·
She is having trouble finding the security fuse. I was digging around and now I'm not sure that her 2002, 4.2 has that security feature. Is this possible?
 

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Yeah ... but not a reason so much as a dead canary in the mineshaft.

You've got something electrical going wacky somewhere.

You're gonna have to confess about YOUR electrical abilities ... reading schematics and bugging out a power loss somewhere.

Tell us if you have a High-Z digital Volt/Ohmmeter, a 12V test light, a Logic probe, soldering ability, a GOOD scanner (read: over $100.00) back-probes, etc.

We're gonna have to get your hands dirty.
 

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let me reposit that the fob has zero to do with starting the engine ... but it can set off the alarm.

i suggest you open the fob and remove the battery .. and if there's another fob --- do the same thing. .... then try to start the vehicle.

Somehow ..... 'way back in the dark corner in the back of my head is the possibility that it is in SECURITY MODE after all.

Let us know how powering-down the fobs works out ... eg: do you EVER see the SECURITY light on --- blinking inside the cluster?
 

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Discussion Starter · #10 ·
Yeah ... but not a reason so much as a dead canary in the mineshaft.

You've got something electrical going wacky somewhere.

You're gonna have to confess about YOUR electrical abilities ... reading schematics and bugging out a power loss somewhere.

Tell us if you have a High-Z digital Volt/Ohmmeter, a 12V test light, a Logic probe, soldering ability, a GOOD scanner (read: over $100.00) back-probes, etc.

We're gonna have to get your hands dirty.
I'm good with schematics and chasing down power issues. I have a good Fluke, test light, a decent scanner, once I activate the Chevy module though i dont have two way ability. I don't know what you mean by "logic probe" and my soldering skills are on par with my wood working skills. I can make a basic box, but it won't be accurate, nor pretty. If you are talking about soldering on a circuit board, that ain't happenin'. I can backprobe and I have a couple mile's worth of test wires with a wide array of connector ends. One thing I lack is an amp clamp, and after leaving my Power Probe on top of my service truck, I don't have that anymore, either. But the Matco Truck will be by tomorrow.

So, it sounds like the instrument panel is possibly a symptom of her electrical issues, but not the cause of the no crank.

I kinda want to send that in to get it repaired so that it is no longer a variable. I hate variables. I also think she should replace the crank relay to eliminate that one as well. The relay is cheap and easy; the cluster, not so much.

As I think about this, the car can start and drive without the cluster, so that can't be the cause of the no crank, so I think that I can eliminate that variable. Maybe.

But, right now she is thinking about going to the dark side and taking it to the dealer. I'm trying to talk her out if that. A good independent with firsthand knowledge of trailblazers, or chevys in general would be better. I'm a diesel mechanic that gas spent most of my 30 year career working on excavation equipment, so I just don't have the specific knowledge on this.

Is there any free or cheap resources for wiring diagrams other than the Chilton version of the Chevy wiring?

One of my problems is that she has become convinced that it is a security system issue and has fallen into the confirmation bias trap. She Googles why her car won't start and sees generic articles confirming that the security system can be an issue. But since I'm not an expert with this car, (give me a John Deere 410D backhoe any day) it's difficult for me to unwind that bias.
 

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Discussion Starter · #11 ·
let me reposit that the fob has zero to do with starting the engine ... but it can set off the alarm.

i suggest you open the fob and remove the battery .. and if there's another fob --- do the same thing. .... then try to start the vehicle.

Somehow ..... 'way back in the dark corner in the back of my head is the possibility that it is in SECURITY MODE after all.

Let us know how powering-down the fobs works out ... eg: do you EVER see the SECURITY light on --- blinking inside the cluster?
First, let me apologize here. I seem to be having trouble posting my replies. I think I do, but I go back and see that I didn't.

Anyway...

I want to be certain about your last question. Are you asking if she has ever seen the security light flash, or are you asking if she sees the security light ever flash once the fob is powered down?

Will this point to something specific by removing the battery, or are we just eliminating one more thing?
 

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Discussion Starter · #12 ·
Last thing for tonight, I promise.

I found bulletin #04-06-03-002. This is related to mis-indexing of the ignition switch. I replaced the ignition switch and the symptoms did not change, but maybe it was installed incorrectly before. I will dig some more and try to figure it out.
 

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The security system can overrule the starter and ignition, fuel injection and I also believe it can interfere with the throttle control, radio/stereo and pretty much anything related to the ignition switch-circuit .... and speaking of that starting circuit --- let's run through the ignition switch too for a bit.

Our ignition switches are kinda sortta responsible for a lot of grief in these cars. You may have to run a full diagnostic test on it --- and there are some really nice PREMIUM Members here with access to schematics ... <hint, hint --- I know you're reading this ... Mr Premium Member>

The SECURITY light blinks when it is armed --- like when you get out and hit the electrical switch on the driver's door to lock the vehicle. You'll see it start flashing --- and I believe if you don't exit the vehicle in a timely way, it will start beeping the horn and on my 05 TB it blinks all 4 corners of the lights.

So-o-o-o the question was mostly rhetorical in that no-one has complained of it flashing and I just wondered why --- or why not, really.

Here's a cheap-but-wonderful logic probe that costs $9.95 unless they come from The Ukraine and then you can expect to pay a lot more or not t all if they aren't available any more ... BUT YOU SHOULD GET ONE....

Automotive tire Hand tool Cable Auto part Wire




LINK HERE

.... and I posted a very elementary lesson on how to use it ---emphasis on "ELEMENTARY"

.
 

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Last thing for tonight, I promise.

I found bulletin #04-06-03-002. This is related to mis-indexing of the ignition switch. I replaced the ignition switch and the symptoms did not change, but maybe it was installed incorrectly before. I will dig some more and try to figure it out.
First -- the ignition wiring circuit --- but beware that there are a LOT of modules and computers that have to establish parity with each other to enable cranking/starting these engines ...

Schematic Font Rectangle Slope Parallel



... a little simpler version:
Schematic Rectangle Slope Line Font


.... AND --- yes --- that letter was referencing this gear that has a distinct timing "mark" that must correctly mesh with the counterpart gear...

Automotive lighting Lego Auto part Automotive wheel system Machine
 

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Discussion Starter · #15 ·
I can see where the logic probe is useful, but it appears that a Power Probe has the same capabilities, it just uses sound, rather than the light. Of course, if all I have is a dumb test light and I want to check ground, I just clamp onto the positive terminal and probe the ground side. Of course that is only safe on non computerized circuits, so I can see the definite benefit of the logic probe: it helps keep the smoke in.

Since the Power Probe has the additional capability of applying power easily, I think I'll stick with that for now.

That schematic is the same one that I found for the start circuit and it reminded me that I need to check the transmission switch since Power to the crank relay runs through that and maybe if the ECU is getting a signal that it's in reverse, the keyfob won't work and it won't crank.

I definitely did not follow the manual on replacing the ignition switch and I think that I need to start there to verify my work.

I don't suppose you are in the PDX area, are you?
 

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Hold it a minute -- do you KNOW FOR SURE that the relay is good?

It can click and light up a test probe --- but not be able to carry any current.

I bought a relay tester a few months ago and about 50% of my relays were "questionable" and another 20% were bad.

I was kinda flatfooted at that point --- but I swear they vehicle ran better, stayed cleaner on dirt roads and balanced the air pressure in all four tire when they were replaced.
 

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I can see where the logic probe is useful, but it appears that a Power Probe has the same capabilities, it just uses sound, rather than the light. Of course, if all I have is a dumb test light and I want to check ground, I just clamp onto the positive terminal and probe the ground side. Of course that is only safe on non computerized circuits, so I can see the definite benefit of the logic probe: it helps keep the smoke in.

Since the Power Probe has the additional capability of applying power easily, I think I'll stick with that for now.

That schematic is the same one that I found for the start circuit and it reminded me that I need to check the transmission switch since Power to the crank relay runs through that and maybe if the ECU is getting a signal that it's in reverse, the keyfob won't work and it won't crank.

I definitely did not follow the manual on replacing the ignition switch and I think that I need to start there to verify my work.

I don't suppose you are in the PDX area, are you?
I'm in Hamilton, Montana.

Is "PDX" Philly-Detroit" ? I didn't want to guess about the "X"-part.
 

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I definitely did not follow the manual on replacing the ignition switch and I think that I need to start there to verify my work.
It's usually best to unwind the things you - or anyone else --- has/have done to get back to the root of the original problem and THEN screw it up and diagnose what caused THAT to happen.

I don't like the Power Probe -- because I don't usually power-up any devices to test them.

That may be counterintuitive --- but it's just me.

If I need to power something up --- I grab my Snap-On MT-302 (which used to be just an MCB).

Automotive lighting Gas Audio equipment Auto part Cable

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Discussion Starter · #20 ·
I
Hold it a minute -- do you KNOW FOR SURE that the relay is good?

It can click and light up a test probe --- but not be able to carry any current.

I bought a relay tester a few months ago and about 50% of my relays were "questionable" and another 20% were bad.

I was kinda flatfooted at that point --- but I swear they vehicle ran better, stayed cleaner on dirt roads and balanced the air pressure in all four tire when they were replaced.
I had one of those relays apart a couple weeks ago. It clicked but it didn't have any connection between pin 30 and 87A. Opened it up and when it was energized, there was daylight between the contacts where they should have been touching.

I took a gander at your channel and saw your old Case. It looks like you have done a bunch of custom work to it. Looking good. (For a Case)
 
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