The vehicle power mode master (PMM) is the body control module (BCM). The ignition switch is a low current switch with 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. There are redundancies within the PMM system that can allow operation of certain subsystems when there are faults in the ignition switch circuits. 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 operator's desired power mode and activate specific discrete signals, and serial data messages for the operation of 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 detect 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 that are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the B+ circuit fuse to the ignition switch will open.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Power Mode Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

With a scan tool, access BCM, Power Mode data display list and compare all parameters listed with the corresponding ignition key position. The PMM Power Mode Parameters table below illustrates the correct state of these input parameters in correspondence to the ignition switch position. The circuits which the individual parameters are related to are in parentheses.

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

1. Ignition OFF, disconnect the harness connector at the ignition switch.
2. Verify that a test lamp illuminates between the B+ circuit terminal B and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or a short to ground, and test the ignition switch ignition voltage output circuits for a short to ground.

3. Verify that a test lamp illuminates between the B+ circuit terminal F and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or a short to ground, and test the ignition switch ignition voltage output circuits for a short to ground.

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

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

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

5. Ignition OFF, connect the harness connector at the ignition switch, and disconnect the X 3 harness connector at the BCM.
6. Verify a test lamp illuminates between ignition 1 voltage circuit terminal A19 and ground only in the RUN and START ignition switch positions.

⇒	If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch.

⇒	If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch.

7. Verify a test lamp illuminates between accessory voltage circuit terminal B15 and ground only in the ACCY and RUN ignition switch positions.

⇒	If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch.

⇒	If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch.

8. Verify a test lamp illuminates between ignition 0 voltage circuit terminal A18 and ground only in the UNLOCK, ACCY, RUN and START ignition switch positions.

⇒	If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch.

⇒	If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch.

9. Verify a test lamp illuminates between ignition 3 voltage circuit terminal A20 and ground only in the RUN ignition switch position.

⇒	If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch.

⇒	If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch.

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

Ignition Switch

1. Ignition OFF, disconnect the harness connector at the ignition switch.
2. Verify the resistance between the terminals listed below match for each ignition switch position.

⇒	If not the specified value, replace the ignition switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.