Pinpoint Test L: The Defrost System Will Not Shut Off Automatically
Glass, Frames and Mechanisms
Pinpoint Tests
Pinpoint Test L: The Defrost System Will Not Shut Off Automatically - MKZ
Refer to Wiring Diagram Set 56 (Fusion/Milan/MKZ, Fusion Hybrid/Milan Hybrid), Heated Window for schematic and connector information. 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 sends the defrost request message to the HVAC module over the Controller Area Network (CAN). When the request is received, the HVAC module activates the rear window defrost relay by grounding the rear window defrost relay coil through circuit CH122 (WH/OG). When the rear window defrost relay is activated, power is supplied from the relay through the antenna module to the rear window defrost grid through circuit CRD06 (BN/YE).
- DTC B1C83:14 (Rear Defog Relay: Circuit Short to Ground or Open) - When the HVAC module senses an open or short to ground 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 L: THE DEFROST SYSTEM WILL NOT SHUT OFF AUTOMATICALLY - MKZ
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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L1 CHECK CIRCUIT CRD06 (BN/YE) FOR A SHORT TO VOLTAGE
- Disconnect: Rear Window Defrost Relay.
- Disconnect: Antenna Module C4194B.
- Ignition ON.
- Measure the voltage between antenna module C4194B-1, circuit CRD06 (BN/YE), harness side and ground.
- Is any voltage present?
Yes
REPAIR circuit CRD06 (BN/YE) for a short to voltage. TEST the system for normal operation.
No
GO to L2.
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L2 CHECK THE HVAC MODULE OUTPUT
- 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) and rear window defrost relay socket pin 86.
- Does the test light illuminate?
Yes
GO to L3.
No
INSTALL a new rear window defrost relay. TEST the system for normal operation.
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L3 CHECK CIRCUIT CH122 (WH/OG) FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: HVAC Module C2356A.
- 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 L4.
No
REPAIR short to ground in circuit CH122 (WH/OG). TEST the system for normal operation.
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L4 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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