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

Glass, Frames and Mechanisms

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

Refer to Wiring Diagram Set 56, Heated Window for schematic and connector information [1][2]Diagrams By Number.

Normal Operation

When the engine is running and the defrost switch (integral to the Front Controls Interface Module (FCIM)) is pressed, the FCIM (Front Controls Interface Module) sends the defrost request message to the HVAC module over the Controller Area Network (CAN). The HVAC module activates the rear window defrost relay by grounding the relay coil through circuit CH122 (WH/OG). When the rear window defrost relay is activated, power is supplied from the relay to the rear window defrost grid through circuit CRD17 (GY). Ground is supplied to the rear window defrost grid through circuit GD109 (BK) (Coupe) or GD110 (BK/WH) (Convertible).

- DTC B1C83:12 (Rear Defog Relay: Circuit Short to Battery)- When the HVAC module senses a short to voltage on the rear window defrost relay control circuit, this DTC will set.

This pinpoint test is intended to diagnose the following:

- Wiring, terminals or connectors

- Rear window defrost relay

- HVAC module

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

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

E1 CHECK REAR WINDOW DEFROST GRID POWER CIRCUIT FOR A SHORT TO VOLTAGE

- Disconnect: Rear Window Defrost Relay.

- Disconnect: Rear Window Defrost Grid Power C402A (Coupe) or C402 (Convertible).

- Ignition ON.

- Measure the voltage between rear window defrost grid power C402A-1 (coupe) or C402-1 (convertible), circuit CRD17 (GY), harness side and ground.





Is any voltage present?

Yes
REPAIR circuit CRD17 (GY) for a short to voltage. CLEAR the DTCs. TEST the system for normal operation.

No
GO to E2.

E2 CHECK THE REAR WINDOW DEFROST RELAY

- Start the engine.

- NOTICE: The following step uses a test light to simulate normal circuit loads. Use only the test light recommended in the Special Tools table at the beginning or equivalent. To avoid connector terminal damage, use the Flex Probe Kit for the test light probe connection to the vehicle. Do not use the test light probe directly on any connector.

Connect a 12-volt incandescent test light between rear window defrost relay socket pin 85, circuit CH122 (WH/OG), harness side and rear window defrost relay socket pin 86, circuit CBB39 (VT/WH), harness side.






Does the test light illuminate?

Yes
GO to E3.

No
INSTALL a new rear window defrost relay. CLEAR the DTCs. TEST the system for normal operation.

E3 CHECK CIRCUIT CH122 (WH/OG) FOR A SHORT TO GROUND

- Ignition OFF.

- Disconnect: HVAC module C294A.

- Measure the resistance between rear window defrost relay socket pin 85, circuit CH122 (WH/OG), harness side and ground.





Is the resistance greater than 10,000 ohms?

Yes
GO to E4.

No
REPAIR short to ground in circuit CH122 (WH/OG). CLEAR the DTCs. TEST the system for normal operation.

E4 CHECK FOR CORRECT HVAC MODULE OPERATION

- Disconnect all HVAC module connectors.

- Check for:
- corrosion.

- pushed-out pins.


- Connect all HVAC module connectors and make sure they seat correctly.

- Operate the system and verify the concern is still present.

Is the concern still present?

Yes
INSTALL a new HVAC module. TEST the system for normal operation.

No
The system is operating correctly at this time. Concern may have been caused by a loose or corroded connector. CLEAR the DTCs. TEST the system for normal operation.