PCM issues after 2-1/2 hrs of driving
 

Hope all is well with everyone,

My PCM gives up after driving ~150 miles on warm days. I take the same trip in the early morning hours with no problems once a month. I've had this problem really since I've owned the truck, but it would only occur on 12hr trips to the North, not it's gotten worse.

When the PCM goes down, no gauges, no charging, no cruise control, no A/C. The truck doesn't skip a beat and keeps on running. I've done a few upgrades, but they weren't in place when I was driving on my 12hr trips.

I can shut the truck off, let it sit 5,10, 15 minutes and everything works again, but not for long. I get a couple codes saying the ECM and PCM lost communication, but they go away from the PCM after a couple trips.

I recently put in a reman PCM - no help.
I swapped the ASD rely with another one in the fuse box - no help.

I doubt its a short or bad ground because once it cools, it runs fine.

Am I looking at a bad ECM?

Whats the ASD Relay do? My manual only says to verify the PCM is getting 12v. I can't tell if those 12v are coming from the ECM or some other sensor.

Any suggestions? Thanks all....

Dan

here's a link to ebsco online manuals.
There is some diagrams of the ABS PCM and such.
Use tech as the password and username.
Scroll down to the auto repair manuals and enter your truck info.

EBSCOhost Login

Its usually a harness problem like a corroded pin or water in the connector be sure to clean it well and use dielectric grease.

Thanks
 

I'm putting the truck in the shop with a good group to look at it and can put it on a lift (getting too fat for that these days). I truly appreciate the feedback and will reply with our findings.

Any Updates?

They were able to recreate the problem and traced it to communication lines that run through the instrument cluster. Grounds and 12v lines all stay up when the problem starts. Reman cluster goes in tomorrow and with some luck I'll have the truck to drive Thursday/Friday for my monthly 2 1/2 hr trip North. Hopefully thats it.