Pinpoint Test 6: The Defrost System Is Inoperative

PINPOINT TEST 6: THE DEFROST SYSTEM IS INOPERATIVE

Normal Operation

The rear window defrost relay receives power from the battery junction box (BJB) fuse 35 (10A) on circuit (Y/GY). When the rear window defrost switch is pressed to the ON position, the HVAC module activates the rear window defrost relay, which then supplies 12 volts to the rear window defrost grid on circuit (BR/Y). The rear window defrost grid is grounded through circuit (B/GY).
The HVAC module will deactivate the rear window defrost relay when one of the following conditions is met:

- The rear window defrost switch is pressed when feature is active.
- The ignition switch state is changed from ON to OFF/LOCK.
- The 15-minute timing function is complete.
- DTC B12BE - Heated backlight/mirror relay drive circuit shorted to battery voltage, heated backlight and heated mirrors wire failure, relay drive circuit shorted to battery.
- DTC B12BF - Heated backlight/mirror relay drive circuit open or shorted to ground, heated backlight and heated mirrors wire failure, relay drive circuit open or shorted to ground.

Possible Causes
- Fuse
- Wiring, terminals or connectors
- Rear window defrost relay
- Rear window defrost switch (integral to the HVAC module)
- Rear window defrost grid
- HVAC module

Diagnostic Procedure