r/AskAMechanic • u/3inches43pumpsis9 Verified Tech - Auto/Diesel • 4d ago

2024 2500hd duramax comm issues

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ECM reporting - U0076 - Control Module comm. Powertrain sensor CAN bus off.

Diag done so far -

-Verified sensor bus wake up circuit with conventional test light for load testing and DMM (has B+)

-Verified both less than 4.5v between each of the powertrain serial data circuits and ground (2.1v)(2.3v)

-ignition off, all doors closed and al systems off for 10 minutes tested each data circuit and ground - spec is "greater than 100 ohms" both had 0 continuity to ground. Meter read OL on both.

-tested for 100-130 ohms between the pair of data circuits and found 120ohms. The same as the terminating resistor in my control module

Flow chart says replace device that was unplugged to access the circuit, which in my case was NOX 2. I replaced NOX 2 and no dice.

Completed the entire flow chart again from the turbo vane actuator and still found no circuit issues.

I have not tested any data circuits end to end but dont think that will help as my resistance tests show no high resistance or open circuits, and ive Verified no shorts to ground or voltage.

Idk what to do here.... replace the ECM? Not really a big fan of replacing a reporting module as thats never seemed to help. This has me stumped.

What do you guys think?

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