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Pinpoint Test F: The Defrost System Is Inoperative

WARNING: This page is about a different car, the 2008 Mercury Mariner and 2008 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
  1. F1 CHECK THE REAR WINDOW DEFROST RELAY 
    • Key in OFF position.
    • Disconnect: Rear Window Defrost Relay
    • Carry out the Rear Window Defrost Relay component test. Refer to appropriate COMPONENT TESTING article.
    • Did the rear window defrost relay pass the component test? 
    1. YES  : Go to  F2.
    2. NO  : INSTALL a new rear window defrost relay. CLEAR all DTCs. TEST the system for normal operation.
  2. F2 CHECK THE REAR WINDOW DEFROST RELAY FEED CIRCUITS FOR VOLTAGE 
    • Key in ON position.
    • Measure the voltage between rear window defrost relay pin 3, CBB35 (YE/GY), harness side and ground; and between rear window defrost relay pin 1, circuit CBB35 (YE/GY), harness side and ground.
      • Fig 1: Measuring Voltage
      GF0041796Courtesy of FORD MOTOR CO.
    • Are the voltages greater than 10 volts? 
    1. YES  : Go to  F3.
    2. NO  : VERIFY BJB fuse 35 (10A) is OK, If OK, REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
  3. F3 CHECK CIRCUIT CRD06 (BN/YE) FOR VOLTAGE 
    • Connect: Rear Window Defrost Relay
    • Disconnect: Rear Window Defrost Grid C402a
    • Key in ON position.
    • Press the rear window defrost switch to the ON position.
    • Measure the voltage between rear window defrost grid C402a-1, circuit CRD06 (BN/YE), harness side and ground.
      • Fig 2: Checking Circuit For Voltage
      GF0019271Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  F4.
    2. NO  : INSPECT BJB fuse 2 (30A). If OK, go to  F5 .
  4. F4 CHECK THE GRID GROUND CIRCUIT FOR AN OPEN 
    • Key in OFF position.
    • Disconnect: Rear Window Defrost C402b
    • Measure the resistance between rear window defrost grid C402b-1, circuit GD149 (BK/GY), harness side and ground.
      • Fig 3: Checking Circuit For Open
      GF0019274Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    1. YES  : CARRY OUT the Grid Wire Test . REPAIR the rear window defrost grid or INSTALL a new liftgate glass as necessary. REFER to Window Grid Wire Repair  or Window Glass - Liftgate . TEST the system for normal operation.
    2. NO  : REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
  5. F5 CHECK CIRCUIT CRD06 (BN/YE) FOR AN OPEN 
    • Key in OFF position.
    • Disconnect: Rear Window Defrost Relay
    • Measure the resistance between rear window defrost relay pin 5, circuit CRD06 (BN/YE), harness side and rear window defrost grid C402a-1, circuit CRD06 (BN/YE), harness side.
      • Fig 4: Measuring Resistance
      GF0041797Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  F6.
    2. NO  : REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
  6. F6 CHECK CIRCUIT CH122 (WH/OG) FOR AN OPEN 
    • Disconnect: HVAC module C2357a or C2356a
    • Measure the resistance between HVAC module C2357a-3 or C2356a-3, circuit CH122 (WH/OG), harness side and rear window defrost relay pin 2, circuit CH122 (WH/OG), harness side.
      • Fig 5: Measuring Resistance
      GF0041798Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  F7.
    2. NO  : REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
  7. F7 CHECK CIRCUIT CH122 (WH/OG) FOR A SHORT TO GROUND 
    • Measure the resistance between rear window defrost relay pin 2, circuit CH122 (WH/OG), harness side and ground.
      • Fig 6: Measuring Resistance
      GF0041799Courtesy of FORD MOTOR CO.
    • Is the resistance greater than 10,000 ohms? 
    1. YES  : Go to  F8.
    2. NO  : REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
  8. F8 CHECK CIRCUIT CH122 (WH/OG) FOR A SHORT TO VOLTAGE 
    • Key in ON position.
    • Measure the voltage between rear window defrost relay pin 2, circuit CH122 (WH/OG) harness side ad ground.
      • Fig 7: Measuring Voltage
      GF0041800Courtesy of FORD MOTOR CO.
    • Is voltage present? 
    1. YES  : REPAIR the circuit. CLEAR all DTCs. TEST the system for normal operation.
    2. NO  : Go to  F9.
  9. F9 CHECK FOR CORRECT HVAC MODULE OPERATION 
    • Disconnect all the HVAC module connectors.
    • Check for:
      • corrosion.
      • pushed-out pins.
    • Connect all the HVAC module connectors and make sure they seat correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
    1. YES  : INSTALL a new HVAC module. REFER to MULTIFUNCTION ELECTRONIC MODULES article. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR all DTCs. TEST the system for normal operation.
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