When the rear defog input circuit 292 to the body control module (BCM) is momentarily
switched to ground (as when the rear defog switch is pressed), the BCM will respond
by grounding circuit 193, the coil of the rear defog relay.
This action energizes 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 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 Parameters
| • | The BCM is NOT requesting the rear defrost system. |
| • | The condition exists for 30 seconds. |
Diagnostic Aids
| • | Check for poor connection at the BCM. Inspect harness connectors for backed
out terminals, improper terminal mating, broken connector locks, improperly formed
or damaged terminals and poor terminal to wire connection (terminal crimped over wire
insulation and not conductors). |
| • | Inspect wiring harness for damage. Check for broken or chaffed insulation. |
| • | If fault is suspected to be intermittent, wiggling the harness wiring
may help in locating the fault. |
