I've read that many GM truck owners do a "Big 3 Upgrade" - replacing the main wiring between the battery, alternator and ground. They call it the cheapest, most mandatory upgrade you can perform. Obviously, without an alternator, the process for the Hybrid would be different.

We've already determined that a solid 12v system is essential for the hybrid to work properly, and that communication issues between the TCM and the HCM can cause the P0AC4 and P061B.

Has anyone upgraded the major harnesses in their HyHoe or equivalent? If so, please share what was changed and the effort involved.

Thanks!

 

Have you looked at the ground straps and the THUMB sized red 12V cable coming out of the APM ( solid state alternator )?


That truck has up to 185 amps at any engine speed including 0rpm.


Further. That P061B is not a communication problem, it is an excessive voltage difference measured by HV battery computer among the 20 internal volt meters. ONLY an excessive voltage difference can set that code.

As such that cpu remembers the fault and sends it to the Hybrid computer. The Hybrid sends the P0AC4 to the Engine computer. The Engine computer has a hard wire to the Check Engine Light.


hope that helps.

 

Are you trying to say the OP has a bad hybrid battery as you've mentioned in other threads?

 

Yes P061B is almost ALWAYS bad battery.