Pinpoint Test I: The Defrost System Will Not Shut Off Automatically
Glass, Frames and Mechanisms
Pinpoint Tests
Pinpoint Test I: The Defrost System Will Not Shut Off Automatically
Refer to Wiring Diagram Set 56, Heated Window for schematic and connector information. Diagrams By Number
Normal Operation
When the engine is running and the defrost switch (integral to the HVAC module or Front Controls Interface Module (FCIM) if equipped with navigation system) is pressed, 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 active, the rear window defrost grid will be energized and the rear window defrost status LED will be illuminated. For vehicles equipped with a power sliding rear window, the rear window defrost relay will not activate the rear defrost relay unless the rear sliding window glass is in the fully CLOSED position due to a glass position switch in series with circuit CH122 (WH/OG). For vehicles equipped with navigation system, the FCIM sends the defrost request message to the HVAC module over the Controller Area Network (CAN). Voltage is supplied to the rear window defrost relay through circuits SBB32 (VT/RD) and CBP43 (GY). When the defrost relay is activated, power is supplied from the relay to the rear window defrost grid through circuit CRD06 (BN/YE). Ground is supplied to the rear window defrost grid through circuit (BK).
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Rear window defrost relay
- HVAC module
PINPOINT TEST I: THE DEFROST SYSTEM WILL NOT SHUT OFF AUTOMATICALLY
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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I1 CHECK REAR WINDOW DEFROST GRID POWER CIRCUIT FOR A SHORT TO VOLTAGE
- Disconnect: Rear Window Defrost Relay.
- Disconnect: Rear Window Defrost Grid Power (passenger side terminal).
- Ignition ON.
- Measure the voltage between rear window defrost grid power terminal, harness side and ground.
- Is the voltage greater than 10 volts?
Yes
REPAIR circuit CRD06 (BN/YE) for a short to voltage. TEST the system for normal operation.
No
GO to I2.
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I2 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. 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.
- If equipped, make sure the rear sliding glass is in the fully CLOSED position.
- Start the engine.
- Connect the 12-volt incandescent test light between rear window defrost relay socket pin 2, circuit CH122 (WH/OG) and rear window defrost relay socket pin 1.
- Does the test light illuminate?
Yes
GO to I3.
No
INSTALL a new rear window defrost relay. TEST the system for normal operation.
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I3 CHECK CIRCUIT CH122 (WH/OG) FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: HVAC Module - DATC C228A (with navigation) or C2109A (without navigation) or HVAC Module - EMTC C294A.
- Measure the resistance between rear window defrost relay socket pin 2, circuit CH122 (WH/OG), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to I4.
No
REPAIR short to ground in circuit CH122 (WH/OG). TEST the system for normal operation.
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I4 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. TEST the system for normal operation.
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