The body control module (BCM) is the power mode master responsible for sending the power mode message on the data buses. The BCM monitors Ignition 1 (Run/Crank) and Ignition 2 (Acc/Run) signals from the ignition switch, and the engine run flag (ERF) in order to determine the present power mode. Refer to Body Control System Description and Operation for the applicable power mode look up table.
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 | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the scan tool display Off Awake? | Go to Step 3 | Go to Step 6 |
3 |
Does the scan tool display Run? | 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 scan tool display Crank? | Go to Step 5 | Go to Step 6 |
5 |
Does the scan tool display Accessory? | 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 only the inputs specified for the ignition switch position? | Go to Step 7 | Go to Step 8 | |
Important:: The engine may start during this procedure. Turn the ignition OFF after verifying this power mode.
Is voltage not present on any inputs specified for the ignition switch position? | Go to Step 9 | Go to Step 11 | |
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 and terminal tension 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 and terminal tension at the harness connector of the BCM. 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 Steering Wheel and Column. Did you complete the replacement? | Go to Step 14 | -- |
13 | Replace the BCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 14 | -- |
14 |
Important:: The engine may start during this procedure. Turn the ignition OFF after verifying all power modes.
Does the displayed power mode parameter match the actual ignition switch position? | System OK | Go to Step 2 |