Pinpoint Test 7: The Defrost System Will Not Shut Off Automatically

PINPOINT TEST 7: THE DEFROST SYSTEM WILL NOT SHUT OFF AUTOMATICALLY

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 by grounding circuit (W/O). When activated, the rear window defrost relay supplies 12 volts, to the rear window defrost grid on circuit (BR/Y). The rear window defrost grid is grounded through circuit (B/GY) to ground.
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 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
- Rear window defrost relay
- Wiring, terminals or connectors
- Rear window defrost switch (integral to HVAC module)
- HVAC module

Diagnostic Procedure

Step 1-Step 3:

Step 4: