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  • P0642 Low Voltage At The #2 Sensor Supply Circuit

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    P0642 LOW VOLTAGE AT THE #2 SENSOR SUPPLY CIRCUIT

    When Monitored and Set Condition:

    When Monitored: With the key on.
    Set Condition: Voltage detected on the #2 sensor supply circuit is below a calibrated value.

    • POSSIBLE CAUSES
    • FAN CLUTCH ASSEMBLY
    • (F856) 5-VOLT SHORTED TO GROUND
    • (F856) 5-VOLT SUPPLY SHORTED TO ANOTHER CIRCUIT
    • FAN DTC
    • INTERMITTENT CONDITION
    • ECM

    DIAGNOSTIC PROCEDURE

    1. Disconnect the Fan clutch harness connector.
      NOTE: Check connectors - Clean/repair as necessary.
      With the DRBIII®, read DTCs. Did P0483 set?
      Yes --> Replace the Fan clutch assembly. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Go To 2
    2. Turn the ignition off. Disconnect the ECM harness connector.
      NOTE: Check connectors - Clean/repair as necessary.
      Measure the resistance between the (F856) #2 5-volt supply (fan speed sensor power) circuit in the sensor harness connector and battery negative. Is the resistance greater than 100k Ohms?
      Yes --> Go To 3
      No --> Repair the #2 (F856) 5-volt supply shorted to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    3. Measure the resistance between the sensor (F856) #2 5-volt supply (fan speed sensor power) circuit in the ECM harness connector to all other circuits in the ECM harness connectors Is the resistance greater than 100k Ohms?
      Yes --> Go To 4
      No --> Repair the 5-volt supply shorted to another circuit. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    4. Reconnect the ECM harness connectors. Reconnect the disconnected Fan harness connector. Turn the ignition on. With the DRBIII®, read DTCs. Is DTC P0483 set?
      Yes --> Repair the Fan DTC. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Go To 5
    5. Turn the ignition off. Disconnect the Fan harness connector. Turn the ignition on. Measure the voltage between the sensor (F856) #2 5-volt supply (fan speed sensor power) circuit at the fan clutch harness connector and the fan speed sensor ground. Is the voltage between 4.5 and 5.5 volts?
      Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).

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