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Home >> Ford >> 2006 >> Focus ZX5 SE, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 1447 (Windows And Glass - Glass, Frames And Mechanisms) >> Diagnostic Tests >> Glass, Frames & Mechanisms >> Pinpoint Tests >> Pinpoint Test E: The Defrost System is Inoperative

Pinpoint Test E: The Defrost System is Inoperative

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

Refer to appropriate SYSTEM WIRING DIAGRAMS article, Heated Window for schematic and connector information.

Normal Operation 

The heated rear window is controlled by the HVAC module. The ignition switch must be in RUN for the defrost system to operate. When the rear window defrost button is pressed, the HVAC module provides a ground for the rear window defrost relay coil through circuit 688 (GY/LB). The rear window defrost relay coil is energized, providing battery voltage to the antenna module on circuit 186 (BN/LB). The antenna module then supplies voltage and ground to the heated rear window grid.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST E: THE DEFROST SYSTEM IS INOPERATIVE 

CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
  1. E1 CHECK THE SIGNAL INPUT 
    • Disconnect: Rear Window Defrost Relay
    • Key in ON position.
    • Press the heated rear window control switch to the ON position.
      • Fig 1: Measuring Resistance
      GF0047515Courtesy of FORD MOTOR CO.
    • Measure the resistance between rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and ground.
    • Is the resistance less than 70 ohms? 
    1. YES  : Go to  E4.
    2. NO  : Go to  E2.
  2. E2 CHECK CIRCUIT 688 (GY/LB) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: HVAC module C228b
    • Key in ON position.
      • Fig 2: Measuring Voltage
      GF0047516Courtesy of FORD MOTOR CO.
    • Measure the voltage at rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and ground.
    • Is any voltage indicated? 
    1. YES  : REPAIR the circuit. TEST the system for normal operation.
    2. NO  : Go to  E3.
  3. E3 CHECK CIRCUIT 688 (GY/LB) FOR AN OPEN 
    • Key in OFF position.
      • Fig 3: Measuring Resistance
      GF0047517Courtesy of FORD MOTOR CO.
    • Measure the resistance between rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and HVAC module C228b-20, circuit 688 (GY/LB), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : INSTALL a new HVAC module. REFER to CLIMATE CONTROL SYSTEM - GENERAL INFORMATION & DIAGNOSTICS article. TEST the system for normal operation.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  4. E4 CHECK CIRCUIT 185 (BK) FOR AN OPEN 
      Fig 4: Measuring Voltage
      GF0047518Courtesy of FORD MOTOR CO.
    • Measure the voltage between rear window defrost relay pin 86, circuit 185 (BK), harness side and ground; and between rear window defrost relay pin 30, circuit 185 (BK), harness side and ground.
    • Are the voltages greater than 10 volts? 
    1. YES  : Go to  E5.
    2. NO  : VERIFY the battery junction box (BJB) fuse 107 (40A) is OK. If OK, REPAIR the circuit in question. TEST the system for normal operation.
  5. E5 CHECK THE RELAY OUTPUT TO THE HEATED REAR WINDOW GRID 
    • Key in OFF position.
    • Connect: Rear Window Defrost Relay
    • Disconnect: Heated Rear Window Grid Connector
    • Key in ON position.
    • Press the heated rear window control switch to the ON position.
      • Fig 5: Checking Circuit For Voltage
      GF0013163Courtesy of FORD MOTOR CO.
    • Measure the voltage between the heated rear window grid connector harness side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  E8.
    2. NO  : Go to  E6.
  6. E6 CHECK THE RELAY OUTPUT TO THE ANTENNA MODULE 
    • Key in OFF position.
    • Disconnect: Antenna Module C4221
    • Key in ON position.
    • Press the heated rear window control switch to the ON position.
      • Fig 6: Checking Circuit For Voltage
      GF0013164Courtesy of FORD MOTOR CO.
    • Measure the voltage between antenna module C4221-1, circuit 186 (BN/LB), harness side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : INSTALL a new antenna module. REFER to INFORMATION & ENTERTAINMENT SYSTEMS article. TEST the system for normal operation.
    2. NO  : Go to  E7.
  7. E7 CHECK CIRCUIT 186 (BN/LB) FOR AN OPEN OR SHORT TO GROUND 
    • Key in OFF position.
    • Disconnect: Rear Window Defrost Relay
      • Fig 7: Measuring Resistance
      GF0047519Courtesy of FORD MOTOR CO.
    • Measure the resistance between antenna module C4221-1, circuit 186 (BN/LB), harness side and rear window defrost relay pin 87, circuit 186 (BN/LB), harness side; and between antenna module C4221-1, circuit 186 (BN/LB), harness side and ground.
    • Is the resistance less than 5 ohms between the antenna module and the heated rear window relay; and greater than 10,000 ohms between the antenna module and ground? 
    1. YES  : INSTALL a new heated rear window relay. TEST the system for normal operation.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  8. E8 CHECK THE GROUND FOR THE HEATED REAR WINDOW GRID 
    NOTE: Make sure the accessory delay has timed out.
    • Key in OFF position.
    • Disconnect: Heated Rear Window Grid Ground Connector
      • Fig 8: Checking Circuit For Ground
      GF0013166Courtesy of FORD MOTOR CO.
    • Measure the resistance between the heated rear window grid ground connector, harness side and ground.
    • Is the resistance less than 5 ohms? 
    1. YES  : Preform the heated rear window grid wire test. REFER to the COMPONENT TESTING . REPAIR as necessary. TEST the system for normal operation.
    2. NO  : INSTALL a new antenna module. REFER to INFORMATION & ENTERTAINMENT SYSTEMS article. TEST the system for normal operation.
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