This vehicles power mode master (PMM) is the body control module (BCM). The ignition switch supplies multiple discrete ignition switch signals to the PMM for determination of the power mode. The PMM receives the ignition switch signals, and additionally a reference voltage signal from the BCM, through the ignition switch, and back to the BCM. Other information such as serial data input from other modules and DTCs is also used to determine what power mode signals and information is transmitted by the PMM. The BCM logic uses all this information to identify the operators desired power mode and activate specific discrete signals, and serial data messages for the operation of many different subsystems as necessary. Other 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 will activate relays and other direct outputs of the PMM as needed according to the calculated power mode. Some relays controlled by the BCM are switched ignition voltage outputs the are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the fuse to the ignition switch may open.

The power modes and controls are determined using BCM logic. Comparing the power mode data display parameters listed in Circuit/System Verification will determine if there is a power mode fault.

Schematic Reference

Connector End View Reference

Master Electrical Component List

Description and Operation

Power Mode Description and Operation

Electrical Information Reference

Scan Tool Reference

With a scan tool, compare all parameters listed with the corresponding ignition key position. The PMM Power Mode Parameters table below illustrates the correct state of the System Power Mode parameter and other parameters in correspondence to the actual ignition switch position.

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the ignition switch connector.

Important: The ignition switch component test must be preformed before proceeding with this test to verify the integrity of the switch.

2. Perform the ignition switch component test. The test should pass.

⇒	If the ignition switch fails, replace the ignition switch.

3. Ignition OFF, disconnect BCM connector C1.
4. Ignition ON, test for less than 1.0 volt between ground and the BCM circuits listed below:

•	12-volt reference terminal 25

•	Crank voltage terminal 21

•	Ignition 1 voltage terminal 22

•	Ignition 3 voltage terminal 23

⇒	If more than 1.0 volt, repair the circuit for a short to voltage.

5. Remove the IGN 1 Relay.
6. Test for infinite resistance between ground and BCM circuits listed below:

•	12-volt reference, BCM terminal 25

•	Crank voltage, BCM terminal 21

•	Ignition 1, voltage, BCM terminal 22

•	Ignition 3 voltage, BCM terminal 23

•	Ignition 1 voltage, BCM terminal 3

⇒	If less than infinite, repair the circuit for a short to ground.

7. Test for less than 1.0 ohm of resistance between the BCM and ignition switch on the following circuits:

•	12-volt reference, BCM terminal 25 and ignition switch terminal 4

•	12-volt reference, BCM terminal 25 and ignition switch terminal 6

•	Crank voltage, BCM terminal 21 and ignition switch terminal 5

•	Ignition 1 voltage, BCM terminal 22 and ignition switch terminal 7

•	Ignition 3 voltage, BCM terminal 23 and ignition switch terminal 3

⇒	If greater than 1 ohm, repair the circuit for open/high resistance

8. If all circuits test normal, replace the BCM.

Ignition Switch

Using the Resistance Test below, check the resistance between the pins of the ignition switch listed in each switch position listed.

Perform the Diagnostic Repair Verification after completing the repair.