Normal vehicle class 2 communications and module operations will not begin until the system power mode has been identified. Discrete circuits from the ignition switch are monitored by the power mode master (PMM) module in order to determine the correct power mode. The PMM communicates the system power mode to all class 2 modules on the class 2 serial data line. The body control module (BCM) is the PMM on this vehicle. Use this table if the class 2 power mode does not match the ignition switch position.
The numbers below refer to the step numbers on the diagnostic table.
This step tests for battery voltage on the signal circuits that are not required.
This step tests for no battery voltage on the required signal circuits.
If any ignition switch parameters that should be inactive in the present ignition switch position are active, 2 ignition switch signal circuits may be shorted together.
This step eliminates open circuits as the cause of the malfunction.
Step | Action | Yes | No |
---|---|---|---|
Schematic Reference: Body Control System Schematics Connector End View Reference: Computer/Integrating Systems Connector End Views DEFINITION: The class 2 power mode displayed on the scan tool does not match the ignition switch position. | |||
1 |
Does the displayed power mode parameter match the actual ignition switch position? | Go to Step 2 | Go to Step 6 |
2 |
Does the displayed power mode parameter match the actual ignition switch position? | Go to Step 3 | Go to Step 6 |
3 |
Does the displayed power mode parameter match the actual ignition switch position? | Go to Step 4 | Go to Step 6 |
4 |
Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
Does the displayed power mode parameter match the actual ignition switch position? | Go to Step 5 | Go to Step 6 |
5 |
Does the displayed power mode parameter match the actual ignition switch position? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 6 |
Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
Is voltage present on any of the inputs that were specified as Inactive for the ignition switch position? | Go to Step 8 | Go to Step 7 | |
Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
Is voltage present on every input specified as Active for the ignition switch position? | Go to Step 11 | Go to Step 9 | |
Did you find and correct the condition? | Go to Step 14 | Go to Step 10 | |
Did you find and correct the condition? | Go to Step 14 | Go to Step 10 | |
10 | Inspect for poor connections at the harness connector of the ignition switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 12 |
11 | Inspect for poor connections at the harness connector of the PMM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 13 |
12 | Replace the ignition switch. Refer to Ignition and Start Switch Replacement in Instrument Panel, Gages and Console. Did you complete the replacement? | Go to Step 14 | -- |
13 | Replace the PMM. Refer to Control Module References . Did you complete the replacement? | Go to Step 14 | -- |
14 |
Does the displayed power mode parameter match the actual ignition switch position? | System OK | Go to Step 1 |