Intermittent Serial Data Problem

[Fless]

For a parasitic draw I would suggest NOT jumping to the "pull the fuse" method. The small fuses have test points on top of them and the voltage drop can be measured when there is current draw. Powerprobe's web site has conversion charts that will estimate the actual amp draw based on the fuse size and voltage drop. https://www.powerprobe.com/na/en/download-list

Pulling fuses, then reinserting them can wake modules that were previously asleep, making for a nightmare when testing. South Main Auto has a few, and others are available.

There are many good YouTube videos on efficient testing methods for parasitic draw.

 

[TJ Baker]

No, but I just borrowed a scanner that might be able to help. It's not bidirectional and I can't start working on the truck until next week, but from all the different ideas I've seen I'm feeling confident that I'll be able to track it down. The fact that there is a power draw might actually help.

Well, feel free to give a shout out if you need.

Here's a little look at the sort of stuff I do with a $15 OBD2 adapter..





This is what J1850VPW serial data actually looks like.
Ever heard of SOH (state of health) messages?
There's at least 10 or more of them here among the normal chatter in this screenshot.

Line 1: BCM sends bus wake up message
Line 2: BCM announces current Power Mode
Line 3: PCM announces the position of the transmission range selector.
Line 4: PCM announces engine is not running
Line 5: PCM sends SOH message
Line 6: IPC sends SOH message
Line 7: IPC acknowledges Transmission Range selection
Line 8: Onstar module sends SOH message
Line 9: RCC module requests current Power Mode
Line 10: BCM sends SOH message
Yada, Yada, Yada......

 

[BigDogYJ]

are you certain it’s a loss of data issue? Have you confirmed powers and grounds for ecm/pcm and bcm? Key grounding points are below driver headlight behind bumper is where ecm is grounded. And under dash cover at bottom of a pillar up against the windshield is where the bcm is grounded.

I only mention it because I started tracking what I thought was a class 2 issue years ago only to find I had an intermittent ground that solved the problem.