Pinpoint Test L: The Defrost System is Inoperative
Glass, Frames and Mechanisms
Pinpoint Test L: The Defrost System is Inoperative - MKZ
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). When the request is received, the HVAC module activates the rear window defrost relay which supplies voltage through the antenna module to the rear window defrost grid.
- DTC B1C83:12 (Rear Defog Relay: Circuit Short to Battery)- sets when the HVAC module detects a short to voltage on the rear window defrost relay control circuit.
- DTC B1C83:14 (Rear Defog Relay: Circuit Short to Ground or Open)- sets when the HVAC module detects an open or short to ground on the rear window defrost relay control circuit.
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Rear window defrost relay
- Wiring, terminals or connectors
- HVAC module
- FCIM (Front Controls Interface Module)
- Antenna module
- Rear window defrost grid
PINPOINT TEST L : THE DEFROST SYSTEM IS INOPERATIVE - 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.
L1 CHECK FOR VOLTAGE TO THE REAR WINDOW DEFROST GRID
- Disconnect: Antenna Module C4194B.
- Start the engine.
- Activate the rear defrost switch and measure the voltage between antenna module C4194B-1, circuit CRD06 (BN/YE), harness side and ground.
Is the voltage greater than 10 volts?
Yes
INSPECT antenna module jumper harness and rear window defrost grid ground circuit for damage and REPAIR as necessary. If jumper harness and defrost grid ground wire are OK, INSTALL a new antenna module. TEST the system for normal operation.
No
GO to L2.
L2 CHECK FOR VOLTAGE TO THE REAR WINDOW DEFROST RELAY
- Ignition OFF.
- Disconnect: Rear Window Defrost Relay.
- Ignition ON.
- Measure the voltage between rear window defrost relay socket pin 86 and ground; and between rear window defrost relay socket pin 30 and ground.
Is the voltage greater than 10 volts for both measurements?
Yes
GO to L3.
No
VERIFY Battery Junction Box (BJB) fuse 6 (40A) and Smart Junction Box (SJB) fuse 45 (5A) are OK. If OK, REPAIR the circuit. 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. TEST the system for normal operation. [1][2]Diagrams By Number
L3 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 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.
- Start the engine.
- Activate the rear window defrost switch.
- 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 L4.
No
GO to L5.
L4 CHECK THE REAR WINDOW DEFROST RELAY
- Carry out the rear window defrost relay component test.
Did the rear window defrost relay pass the component test?
Yes
REPAIR open in circuit CRD06 (BN/YE). CLEAR the DTCs. TEST the system for normal operation.
No
INSTALL a new rear window defrost relay. CLEAR the DTCs. TEST the system for normal operation.
L5 CHECK THE REAR WINDOW DEFROST SWITCH (CC_SW_R_DEF) PID
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: DataLogger- FCIM (Front Controls Interface Module).
- Monitor the FCIM (Front Controls Interface Module) CC_SW_R_DEF PID while pressing and releasing the rear window defrost switch.
Does the PID agree with the rear window defrost switch status?
Yes
GO to L6.
No
INSTALL a new FCIM (Front Controls Interface Module). CLEAR the DTCs. TEST the system for normal operation.
L6 CHECK THE REAR WINDOW DEFROST RELAY CONTROL CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: HVAC Module C2356A.
- Measure the resistance between rear window defrost relay socket pin 85, circuit CH122 (WH/OG), harness side and HVAC module C2356A-12, circuit CH122 (WH/OG), harness side.
Is the resistance less than 5 ohms?
Yes
GO to L7.
No
REPAIR the circuit. TEST the system for normal operation.
L7 CHECK FOR CORRECT HVAC MODULE OPERATION
- Disconnect all HVAC module electrical connectors.
- Check for:
- corrosion.
- pushed-out pins.
- Connect all HVAC module electrical 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.