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Pinpoint Test T: Dual Generator Upper Fault Detected (P0620)

WARNING: This page is about a different car, the 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
  1. T1 CHECK THE UPPER GENERATOR CONNECTIONS 
    • Key in OFF position.
    • Disconnect: Upper Generator C102c and C102a.
    • Check the upper generator connectors for damage and correct connection.
    • Connect: Upper Generator C102c and C102a.
    • Are the upper generator connectors OK and correctly connected? 
    • Yes  : GO to T2.
    • No  : REPAIR the connections as necessary. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  2. T2 CHECK THE UPPER GENERATOR B+ VOLTAGE 
    • Measure the voltage between the B+ terminal of the upper generator C102c, circuit 36 (YE/WH) harness side and ground.
      Fig 1: Checking Upper Generator B+ Voltage
      G03910828Courtesy of FORD MOTOR CO.
    • Is the voltage equal to battery voltage? 
    • Yes  : GO to T3.
    • No  : CHECK the B+ circuit 36 (YE/WH) including the fusible links. REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  3. T3 CHECK THE UPPER GENERATOR A CIRCUIT FOR VOLTAGE 
    • Disconnect: Upper Generator C102a.
    • With the upper generator connector disconnected, measure the voltage between the upper generator C102a pin 3, A circuit 35 (OG/LB), harness side and ground.
      Fig 2: Measuring Voltage Between Connector And Ground
      G03930849Courtesy of FORD MOTOR CO.
    • Is the voltage equal to battery voltage? 
    • Yes  : GO to T4.
    • No  : CHECK the upper generator A circuit 35 (OG/LB) including the fusible links. REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  4. T4 CHECK THE UPPER GENERATOR I CIRCUIT FOR VOLTAGE 
    • Key in ON position.
    • With the key ON, engine OFF, measure the voltage between the upper generator connector C102a pin 1, I circuit 904 (LG/RD), harness side and ground.
      Fig 3: Checking Upper Generator I Circuit For Voltage
      G03924850Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    • Yes  : GO to  T6.
    • No  : GO to T5.
  5. T5 CHECK THE UPPER GENERATOR I CIRCUIT FOR AN OPEN OR SHORT TO GROUND 
    • Key in OFF position.
    • Disconnect: PCM C1381c.
    • With the key OFF and the upper generator C102a still disconnected, check the resistance between the generator C102a pin 1, I circuit 904 (LG/RD) harness side and the PCM C1381c pin 1, circuit 1183 (WH/YE) harness side; and between the generator C102a pin 1, I circuit 904 (LG/RD) harness side and ground.
      Fig 4: Checking Upper Generator I Circuit For Open Or Short To Ground
      G03924872Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms between the generator and the PCM, and greater than 10,000 ohms between the generator and ground? 
    • Yes  : GO to  T8.
    • No  : REPAIR I circuit 1183 (WH/YE) / 904 (LG/RD). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  6. T6 CHECK THE UPPER GENERATOR VOLTAGE 
    • Connect: PCM C1381c.
    • Disconnect: Lower Generator C1251a.
    • Connect: Upper Generator C102a.
    • Key in START position.
      • NOTE: After starting the engine, wait at least 2 minutes for the glow plugs to stop cycling.
      Fig 5: Measuring Battery Voltage
      G03879700Courtesy of FORD MOTOR CO.
    • With the engine running, measure the voltage at the battery.
    • Is the voltage greater than 13 volts? 
    • Yes  : GO to T7.
    • No  : INSTALL a new upper generator. REFER to GENERATOR AND REGULATOR . CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  7. T7 CHECK THE UPPER GENERATOR OUTPUT 
    • Yes  : The system is operating normally. CONNECT all the connectors. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
    • No  : INSTALL a new upper generator. REFER to GENERATOR AND REGULATOR . CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  8. T8 CHECK FOR CORRECT PCM OPERATION 
    • Disconnect all the PCM connectors.
    • Check for:
      • corrosion
      • pushed-out pins
    • Connect all the PCM 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 PCM. REFER to ELECTRONIC ENGINE CONTROLS - DIESEL ENGINE . CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
    • No  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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