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Begin the diagnosis of the body control system by performing the diagnostic system check for the system in which the customer concern is apparent.
The diagnostic system check will direct you to the correct procedure for diagnosing the system and where the procedure is located.
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Test Description
The numbers below refer to the step numbers on the diagnostic table.
- 6. This step tests for battery voltage on the signal circuits that are not required.
- 7. This step tests for no battery voltage on the required signal circuits.
- 8. 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.
- 9. This step eliminates open circuits as the cause of the malfunction.
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Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the BCM fail to send a power mode message. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power mode.