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?