Serial Data Power Mode

WARNING: This page is about a different car, the 2003 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle, the PMM is the DIM. The PMM receives 4 signals from the ignition switch.

To determine the correct power mode the PMM uses inputs from the following circuits:

Accessory voltage
Ignition 3 voltage
Off/Run/Crank voltage
Run/Crank voltage

Fig 1: 4-Wire Ignition Switch Table

Courtesy of GENERAL MOTORS CORP.