Pinpoint Test F: The Defrost System is Inoperative
Glass, Frames and Mechanisms
Pinpoint Tests
Pinpoint Test F: The Defrost System is Inoperative
Refer to Wiring Diagram Set 56, Heated Window for schematic and connector information. Diagrams By Number
Normal Operation
The rear window defrost relay receives power from the Battery Junction Box (BJB) fuse 31 (10A) on circuit CBB31 (BU/OG). When the rear window defrost switch is pressed to the ON position and the engine is running, the HVAC module activates the rear window defrost relay by grounding circuit CH122 (WH/OG). When activated, the rear window defrost relay supplies voltage to the rear window defrost grid on circuit CBB02 (GN). The rear window defrost grid is grounded through circuit GD110 (BK/WH).
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) - Sets when a short to voltage is detected in the relay control circuit.
- DTC B12BF (Heated Backlight/Mirror Relay Drive Circuit Open or Shorted to Ground) - Sets when an open or short to ground is detected in the relay control circuit.
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- Rear window defrost relay
- Rear window defrost switch (integral to the HVAC module)
- Rear window defrost grid
- HVAC module
PINPOINT TEST F: THE DEFROST SYSTEM IS INOPERATIVE
NOTICE: Use the correct probe adapter(s) from the Flex Probe Kit when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
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F1 CHECK CIRCUIT CBB02 (GN) FOR VOLTAGE
- Disconnect: Rear Window Defrost Grid C402A.
- Start the engine.
- Activate the rear window defrost switch.
- Measure the voltage between rear window defrost grid C402A-1, circuit CBB02 (GN), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to F2.
No
VERIFY BJB fuse 2 (30A) is OK. If OK, GO to F3.
If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation. Diagrams By Number
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F2 CHECK THE GRID GROUND CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: Rear Window Defrost C402B.
- Measure the resistance between rear window defrost grid C402B-1, circuit GD110 (BK/WH), harness side and ground.
- Is the resistance less than 5 ohms?
Yes
CARRY OUT the Grid Wire component test. Component Tests and General Diagnostics REPAIR the rear window defrost grid or INSTALL a new rear window glass as necessary. REFER to Window Grid Wire Repair Window Grid Wire Repair or Window Glass - Rear Window Glass - Rear. TEST the system for normal operation.
No
REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
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F3 CHECK THE REAR WINDOW DEFROST RELAY FEED CIRCUITS FOR VOLTAGE
- Disconnect: Rear Window Defrost Relay.
- Ignition ON.
- Measure the voltage between rear window defrost relay socket pin 3, and ground; and between rear window defrost relay socket pin 1, circuit CBB31 (BU/OG), and ground.
- Are the voltages greater than 10 volts?
Yes
GO to F4.
No
VERIFY BJB fuse 35 (10A) is OK, If OK, REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short. REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation. Diagrams By Number
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F4 CHECK THE HVAC MODULE
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. 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.
- Start the engine.
- Activate the rear window control switch.
- Connect a 12-volt incandescent test light between rear window defrost relay socket pin 1, circuit CBB31 (BU/OG) and rear window defrost relay socket pin 2, circuit CH122 (WH/OG).
- Does the test light illuminate?
Yes
GO to F5.
No
GO to F6.
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F5 CHECK THE REAR WINDOW DEFROST RELAY
- Ignition OFF.
- Carry out the rear window defrost relay component test.
- Did the rear window defrost relay pass the component test?
Yes
REPAIR open in circuit CBB02 (GN). CLEAR the DTCs. TEST the system for normal operation.
No
INSTALL a new rear window defrost relay. CLEAR all DTCs. TEST the system for normal operation.
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F6 CHECK CIRCUIT CH122 (WH/OG) FOR AN OPEN
- Key OFF.
- Disconnect: HVAC Module C2357A.
- Measure the resistance between HVAC module C2357A-3, circuit CH122 (WH/OG), harness side and rear window defrost relay socket pin 2, circuit CH122 (WH/OG).
- Is the resistance less than 5 ohms?
Yes
GO to F7.
No
REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
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F7 CHECK FOR CORRECT HVAC MODULE OPERATION
- Disconnect all the HVAC module connectors.
- Check for:
- corrosion.
- pushed-out pins.
- Connect all the 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. The concern may have been caused by a loose or corroded connector. CLEAR all DTCs. TEST the system for normal operation.
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