Communication and Hosted Diagnostics
WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
The APM has internal diagnostic tests that run at both power-up and during operation. All DTCs from the APM are reported to and hosted by the HPCM. The APM communicates directly only with the HPCM and only on the high speed hybrid GMLAN communication circuit.