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Pinpoint Test L: The Defrost System Is Inoperative - MKZ

WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: 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.
  1. 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.
      Fig 1: Checking Voltage To The Rear Window Defrost Grid
      G07789092Courtesy of FORD MOTOR CO.
    • 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.
  2. 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.
      Fig 2: Measuring Voltage Between Rear Window Defrost Relay Socket Pin 86, 30 And Ground
      G07789093Courtesy of FORD MOTOR CO.
    • 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 SYSTEM WIRING DIAGRAMS article, to identify the possible causes of the circuit short. REPAIR the circuit. TEST the system for normal operation.

  3. L3 CHECK THE HVAC MODULE 
    NOTE: 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 of this service information 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.
      Fig 3: Connecting 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
      G07789094Courtesy of FORD MOTOR CO.
    • Does the test light illuminate? 
    • Yes  : Go to  L4.
    • No  : Go to  L5.
  4. L4 CHECK THE REAR WINDOW DEFROST RELAY 
    • 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.
  5. 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.
    • Monitor the FCIM 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? 
  6. 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.
      Fig 4: Checking Rear Window Defrost Relay Control Circuit For Open
      G07789095Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : Go to  L7.
    • No  : REPAIR the circuit. TEST the system for normal operation.
  7. 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. Refer to CLIMATE CONTROL -- FUSION, MILAN & MKZ article. 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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