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Pinpoint Test H: The Defrost System Is Inoperative

WARNING: This page is about a different car, the 2014 Ford F-150. 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. H1 CHECK THE REAR WINDOW DEFROST GRID VOLTAGE 
    • Disconnect: Rear Window Defrost Grid Power (passenger side outer terminal).
    • Start the engine.
    • Activate the rear window defrost switch and measure the voltage between rear window defrost grid power terminal, harness side and ground.
      Fig 1: Measuring Voltage Between Rear Window Defrost Grid Power Terminal And Ground
      G07934854Courtesy of FORD MOTOR CO.

    Is the voltage greater than 10 volts? 

    • Yes  : GO to H2  .
    • No  : GO to  H5.
  2. H2 CHECK THE REAR WINDOW DEFROST GRID GROUND 
    • Ignition OFF.
    • Disconnect: Rear Window Defrost Grid Ground (Driver Side Terminal).
    • Measure the resistance between rear window defrost grid ground terminal, harness side and ground.
      Fig 2: Measuring Resistance Between Rear Window Defrost Grid Ground Terminal And Ground
      G07934855Courtesy of FORD MOTOR CO.

    Is the resistance less than 5 ohms? 

    • Yes  : If equipped with a power sliding rear window, GO to H3  .

      If not equipped with a power sliding rear window, CARRY OUT the GRID WIRE TEST . ATTEMPT to REPAIR the rear window defrost grid, REFER to WINDOW GRID WIRE REPAIR . If not repairable, INSTALL a new rear window glass assembly. REFER to WINDOW GLASS - REAR . TEST the system for normal operation.

    • No  : REPAIR the circuit. TEST the system for normal operation.
  3. H3 CHECK THE REAR WINDOW DEFROST SWITCH LED OPERATION 
    • Ignition OFF.
    • Disconnect: Rear Window Defrost Grid Inline (Passenger Side) C3368  .
    • Install a fused jumper wire between rear window defrost grid inline C3368-1  , circuit CH122 (WH/OG), harness side and C3368-2  , circuit CRD06 (BN/YE), harness side.
      Fig 3: Checking Rear Window Defrost Switch LED Operation
      G07965646Courtesy of FORD MOTOR CO.
    • Start the engine.
    • Activate the rear window defrost switch.

    Does the rear window defrost switch LED illuminate? 

  4. H4 CHECK THE REAR WINDOW DEFROST FEEDBACK CIRCUIT FOR AN OPEN 
    • Ignition OFF.
    • Disconnect: HVAC Module - EATC C228B  or HVAC Module - Electronic Manual Temperature Control (EMTC) C294A  .
    • Measure the resistance between rear window defrost grid inline C3368  and the HVAC module.
      • For vehicles equipped with EMTC  , measure the resistance between rear window defrost grid inline C3368-1  , circuit CH122 (WH/OG), harness side and HVAC module - EMTC C294A-22  , circuit CH122 (WH/OG), harness side.
      • For vehicles equipped with EATC  , measure the resistance between rear window defrost grid inline C3368-1  , circuit CH122 (WH/OG), harness side and HVAC module - EATC C228B-7  , circuit CH122 (WH/OG), harness side.
        Fig 4: Measuring Resistance Between Rear Window Defrost Grid Inline C3368 And HVAC Module
        G08344108Courtesy of FORD MOTOR CO.

    Is the resistance less than 5 ohms? 

    • Yes  : GO to  H10.
    • No  : REPAIR the circuit. TEST the system for normal operation.
  5. H5 CHECK THE POWER TO THE RELAY 
    • Ignition OFF.
    • Disconnect: Rear Window Defrost Relay.
    • Ignition ON.
    • Measure the voltage between rear window defrost relay socket pin 1, circuit CBB54 (VT/OG), harness side and ground; and between pin 3, circuit SBB32 (VT/RD), harness side and ground.
      Fig 5: Measuring Voltage Between Rear Window Defrost Relay Socket Pin 1, Circuit CBB54 (VT/OG) And Ground
      G06173672Courtesy of FORD MOTOR CO.

    Is the voltage greater than 10 volts for both measurements? 

    • Yes  : GO to H6  .
    • No  : VERIFY Battery Junction Box (BJB) fuse(s) 32 (40A) and 54 (5A) are OK. If OK, REPAIR the circuit(s). TEST the system for normal operation. If not OK, REFER to the OEM WIRING DIAGRAMS to identify the possible causes of the circuit short. REPAIR the circuit. TEST the system for normal operation.
  6. H6 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 article. 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 the 12-volt incandescent test light between rear window defrost relay socket pin 2, circuit CRD02 (BN/BU) and rear window defrost relay socket pin 1, circuit CBB54 (VT/OG).
      Fig 6: Checking HVAC Module
      G06458883Courtesy of FORD MOTOR CO.

    Does the test light illuminate? 

    • Yes  : GO to H7  .
    • No  : For vehicles equipped with the 4.2-inch (107mm) or 8-inch (203mm) display, GO to  H8. For vehicles not equipped with the 4.2-inch (107mm) or 8-inch (203mm) display, GO to  H9.
  7. H7 CHECK THE REAR WINDOW DEFROST RELAY 

    Did the rear window defrost relay pass the component test? 

    • Yes  : REPAIR open in circuit CRD06 (BN/YE). TEST the system for normal operation.
    • No  : INSTALL a new rear window defrost relay. TEST the system for normal operation.
  8. H8 CHECK THE REAR DEFROST SWITCH (CC_SW_R_DEF) PID 
    • Ignition ON.
    • Enter the following diagnostic mode on the scan tool: Data Logger - 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 defrost switch status? 

    • Yes  : GO to H9  .
    • No  : INSTALL a new FCIM  . Refer to the appropriate article for the procedure. TEST the system for normal operation.
  9. H9 CHECK THE REAR WINDOW DEFROST RELAY CONTROL CIRCUIT FOR AN OPEN 
    • Ignition OFF.
    • Disconnect: HVAC Module - EATC C228B  or HVAC Module - Electronic Manual Temperature Control (EMTC) C294A  .
    • Measure the resistance between rear window defrost relay and the HVAC module.
      • For vehicles equipped with EATC  , measure the resistance between rear window defrost relay socket pin 2, circuit CRD02 (BN/BU) and HVAC module - EMTC C294A-25  , circuit CRD02 (BN/BU), harness side.
      • For vehicles equipped with EATC  , measure the resistance between rear window defrost relay socket pin 2, circuit CRD02 (BN/BU) and HVAC module - EATC C228A-25  , circuit CRD02 (BN/BU), harness side.
        Fig 7: Measuring Resistance Between Rear Window Defrost Relay And HVAC Module
        G08344111Courtesy of FORD MOTOR CO.

    Is the resistance less than 5 ohms? 

    • Yes  : GO to H10  .
    • No  : REPAIR the circuit. TEST the system for normal operation.
  10. H10 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 HEATING VENTILATION AIR CONDITIONING (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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