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.
In addition to the internal SPI bus communication circuit between the HPCM and each MCM, the MCMs also communicate on the Hi-speed and Hybrid GMLAN communication circuits. The MCM does not store its own diagnostic trouble code (DTC) information. The HPCM will store MCM associated DTC information for retrieval by a scan tool. The scan tool can communicate directly with each MCM in order to retrieve data parameters only.