This vehicles 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 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. Several 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 will open.

Ignition switch is in the RUN position.

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

1. Verify that the following DTCs are not set: U1814, B1428.

⇒	If either of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. With a scan tool, access Body Control Module, 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 (circuits) 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. Inspect for an open Ign Switch fuse. The fuse should be OK.

⇒	If the fuse is open, test the following circuits for a short to ground, if all circuits test OK, replace the BCM.

•	Battery positive voltage of the ignition switch

•	Accessory voltage

•	Off/Run/Crank voltage

•	Ignition 1 voltage

•	Accessory wakeup serial data (BCM output)

•	Run/crank ignition 1 voltage (BCM output)

2. Disconnect the harness connector at the ignition switch.
3. Verify that a test lamp illuminates between the B+ circuit terminal 4 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

Important: The ignition switch component test must be preformed 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, disconnect the X 1 harness connector at the BCM, test for less than 1.0 volt between the following circuit terminals of the BCM and ground.

•	Ignition key resistor signal terminal 4

•	Off/Run/Crank voltage terminal 2

•	Accessory voltage terminal 21

•	Ignition 1 voltage terminal 14

⇒	If greater than specified, test the circuit for a short to voltage.

6. Test for less than 1.0 ohm of resistance between the BCM and the ignition switch on the following circuit terminals.

•	Ignition key resistor signal, BCM terminal 4 and ignition switch terminal 6

•	Off/Run/Crank voltage, BCM terminal 2 and ignition switch terminal 5

•	Accessory voltage, BCM terminal 21 and ignition switch terminal 3

•	Ignition 1 voltage, BCM terminal 14 and ignition switch terminal 2

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

7. Test for infinite resistance between the ignition key resistor signal circuit terminal 4 of the BCM and ground.

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

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

Ignition Switch

1. Ignition OFF, disconnect the harness connector at the ignition switch.
2. Using the Resistance Test table below, check the resistance between the terminals of the ignition switch listed in each switch position.

Perform the Diagnostic Repair Verification after completing the repair.