For 1990-2009 cars

### Serial Data Power Mode Master

Power to many of this vehicles circuits is controlled by the module that is designated the power mode master (PMM). This vehicles has 3 PMM, the steering column control module (SCCM), underhood electrical center (UEC), and rear electrical center (REC). The ignition switch is an intergrated part of the SCCM and determins the power mode that will be sent over the serial data circuits to the other modules that need this information. The PMM's will also activate relays and other direct outputs of the PMM as needed. The PMM determines which power mode (Off, Accessory, Run, Crank Request) is required, and reports this information to other modules via serial data. Modules which have switched voltage inputs may operate in a default mode if the PMM serial data message does not match what the individual module can see from its own connections.

The PMM receives ignition switch signals to identify the operators desired power mode. The PMM Power Mode Parameters table below illustrates the correct state of these input parameters (circuits) in correspondence to the ignition switch position:

#### PMM Power Mode Parameters

Ignition Switch Position | Power Mode Transmitted | 'KEY-IN' Status | Accessory Status | Ignition Status | Crank Request
--- | --- | --- | --- | --- | ---
Off Key Out | Off | Inactive | Key Out/ACC | Active/Inactive | Inactive
Off Key IN | Off | Inactive | Key In/Off | Active/Inactive | Inactive
Accessory | Accessory | Active | Active | Active/Inactive | Inactive
Run | Run | Active | Run | Active/Inactive | Active/Inactive
Start | Crank Request | Active | Crank | Active/Inactive | Active

### Relay Controlled Power Mode

The SCCM uses the ignition switch inputs Run/Crank Ignition 1 Voltage, Accessory Voltage, and Ignition 1 Voltage, to distinguish the correct power mode. The SCCM, after determining the desired power mode, will activate the appropriate relays for that power mode.