Dont crank when hot.

[Kun333]

Hi!

After ride, when engine is hot, after 10-30 minuts i'm cant start the engine.

Diagnose - dont have signal from PCM to relay. (Out 39 in C1 blue).

If i ride with open hood or stay with open hood 30-40 minuts - starts okay.

I'll check all wiring, ignition switch is okay. Two fuse block are changed)

I have not confirmed trouble codes U1000, U1096, B2961 and U1255

 

[rockola1971]

Is security light on or flashing when you try to crank when hot and it fails to turn starter over?

 

[Kun333]

Is security light on or flashing when you try to crank when hot and it fails to turn starter over?

You mean check or car with lock?
Everithing work as usual! When key in crank position, all lights are turning off, and security gone away after.

 

[rockola1971]

You mean check or car with lock?
Everithing work as usual! When key in crank position, all lights are turning off, and security gone away after.

What year and vehicle are you dealing with here. You will not get the output out of C1-39 if passlock is not satisfied or just faulty. And C1-39 gives a ground to the start relay coil NOT 12v+ so be mindful of that when sticking a voltmeter on it for troubleshooting.

 

[Kun333]

What year and vehicle are you dealing with here.

Chevy tahoe 2004

 

[rockola1971]

Passlock gives the go ahead and allow engine to stay running after it is started via permissive serial data stream from BCM to PCM.

 

[Kun333]

And why this thing stop to work after 20 min after stop? And start to work after 40 min with open hood?

When passlock working, engine starting but immidiately stopping. In this case icon is on.

And what i can do with this?

 

[Jimmyy]

I would check your cables connections for corrosion or the cable for green death. Use jumper cables to jump around the starter cable and ground cables one at a time. Maybe a can of air to cool the starter or connections.

 

[rockola1971]

And why this thing stop to work after 20 min after stop? And start to work after 40 min with open hood?

When passlock working, engine starting but immidiately stopping. In this case icon is on.

And what i can do with this?

I havent seen enough of the protocol that passlock uses so im not sure if it has to give a constant go ahead via BCM to the PCM or its a one and done once started and go ahead happens. Like the guy above said it wouldnt hurt to check battery cables over real good. Corrosion could cause this symptom as well. If it ends up being the passlock module you will be lucky since its an hour work to change out and cost like $30 for the part.
I would definitely reverify the 12v across the start relay when the fail to start happens. Stick red meter lead on battery positive and black lead on C1 39 or maybe even rig a wire up on start relay socket connection that leads to D12 on the schematic to rule out everything in between D12 and C1 39. Remember this start relay is GROUND seeking. Not 12V positive seeking.

 

[rockola1971]

"I have not confirmed trouble codes U1000, U1096, B2961 and U1255" What does this mean? You are getting these codes OR you havent confirmed yet that you ARE NOT getting these codes?

 

[Kun333]

"I have not confirmed trouble codes U1000, U1096, B2961 and U1255" What does this mean? You are getting these codes OR you havent confirmed yet that you ARE NOT getting these codes?

This codes are in memory, but not realize check lamp. Its mean they are episidically.

 

[Kun333]

Checked yellow and green wires from bcm to pcm - it's okay.
Can problem be in crankshaft sensor or something whitch can become hot and say "not now"? Because problem is only when engine normal hot. PCM?

 

[MassHoe04]

Bad crank position or cam sensor could cause no start, but would not prevent the engine from turning over.

To be clear...

Are you experiencing:

No Crank/No Start after warm-up?
(No starter action, engine does not turn over, does not fire up or run)

-or-

Crank/No Start after warm-up?
(Starter works, engine turns over, but and engine does not fire up or run)

 

[rockola1971]

Bad crank position or cam sensor could cause no start, but would not prevent the engine from turning over.

To be clear...

Are you experiencing:

No Crank/No Start after warm-up?
(No starter action, engine does not turn over, does not fire up or run)

-or-

Crank/No Start after warm-up?
(Starter works, engine turns over, but and engine does not fire up or run)

And also to confirm with the above......

Does engine only fail to start or turn over (whichever symtpom(s) you are having, does this only happen once engine is shutoff or is the engine dying on its own and fail to start or turnover?

"Turns over" Means engine is being spun by the starter. (starter is working correctly)
Fails to fire Means engine turns over but does not start (no spark and/or fuel problem)
Fails to turn over Means engine is not being spun by the starter (so there is starter or starter circuit wiring problem)

 

[Kun333]

Took the pcm from nest, and placed it near fuse box. When its cold - its okay, when its hot - its not okay. Take a ride, open hood, sthrow it on fender, 3 min and we ready to go again!)

Friend says i'm need a new PCM with the arabic proramm, to disable pk3!)

 

[OR VietVet]

Sure would be good to get info back about cables inspection and is it a crank and no start or no crank problem at all times the problem occurs, or did I miss the answers?

 

[Kun333]

I have this problem.

 

[OR VietVet]

Which is exactly why I have at least 1 if not 2, of each relay in that box that I carry with me. Never needed yet but is cheap enough to get and keep in case.

 

[rockola1971]

Took the pcm from nest, and placed it near fuse box. When its cold - its okay, when its hot - its not okay. Take a ride, open hood, sthrow it on fender, 3 min and we ready to go again!)

Friend says i'm need a new PCM with the arabic proramm, to disable pk3!)

That sounds like your output transistor in your PCM is electrically opening up when it gets hot. Not very common but not impossible., Ive seen a transistor open when hot and even short when hot then "heal" itself when cooled down. Usually they eventually fail totally open or shorted in due time though. I would grab a PCM off ebay or car-part.com that matches your PCM part# and swap out and see if problem goes away. This problem if in the PCM will be hard to prove without knowing what all permissions are needed to get that output transistor to give a ground to the start relay and be able to monitor them all to see if they are there.

 

[Kun333]

That sounds like your output transistor in your PCM is electrically opening up when it gets hot. Not very common but not impossible., Ive seen a transistor open when hot and even short when hot then "heal" itself when cooled down. Usually they eventually fail totally open or shorted in due time though. I would grab a PCM off ebay or car-part.com that matches your PCM part# and swap out and see if problem goes away. This problem if in the PCM will be hard to prove without knowing what all permissions are needed to get that output transistor to give a ground to the start relay and be able to monitor them all to see if they are there.

Yes, I came to the same conclusion. It is difficult to understand which of the transistors is open the output. Its 6 pcs in board. And I can't find "ior336a" in local stores.
It can also be a track inside the board.
I'll buy another PCM one of these days and take a look.
Maybe wherever there are any explanations about of the PCM.