Chart 6 - B0286 - Electric Rear Defrost Circuit High

Diagnostic Chart 6:

Schematic:

CIRCUIT DESCRIPTION
When the rear defrost input circuit 292 to the BCM (Body Control Module) is momentarily switched to ground (as when the rear defrost switch is pressed), the BCM will respond by grounding circuit 193, the coil of the rear defrost relay.

This action energized the rear defrost relay providing power to circuit 293-rear defrost heater elements, circuit 683-heated mirror relay coil and circuit 683-rear defrost LED telltale. Momentarily switching circuit 292 to ground again will result in the BCM turning the rear defrost relay "OFF".

The first time in an ignition cycle that the rear defrost is activated, rear defrost will remain "ON" for 15 minutes or until the ignition switch is turned "OFF". If rear defrost is activated again during the same ignition cycle, rear defrost will remain "ON" for 7 1/2 minutes or until the ignition switch is turned "OFF".

DTC SET CONDITIONS:
^ Ignition in "RUN" position.
^ Circuit 193 shorted to battery voltage.
^ BCM is commanding the rear defrost system to the "ON" state.

DIAGNOSTIC AIDS:
^ When a shorted to battery voltage condition exists in circuit 193 and the BCM has been requested to activate the rear defrost system, the BCM will attempt to switch the 193 circuit to ground. High current flow will result and the BCM output will go into a protective state. The BCM output will not allow itself to be activated for as much as 3 minutes.
^ Inspect wiring harness for damage. Check for broken or chaffed insulation.
^ If fault is suspected to be intermittent, wiggling harness wiring may help in locating fault.