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Home › Jeep › 2021 › Cherokee Trailhawk › Repair and Diagnosis › Engine Performance › System › 3.2L - DTCS P054C To P1129 › DTC Troubleshooting › P0622-Generator Field Control Circuit/Open › Diagnostic Test

Diagnostic Test

  1. CHECK FOR AN ACTIVE DTC 
    1. Start the engine and allow it to idle.
      WARNING:

      When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

    2. With the scan tool, read DTCs and record on the repair order.

      Is the DTC active or pending?

      Yes 

      • Go To  2

      No 

  2. CHECK THE ALTERNATOR DUTY CYCLE 
    1. With the scan tool, check the Duty Cycle reading for the Alternator.
      NOTE:

      During normal operation the typical duty cycle of the field control at idle with minimal loads is approximately 35-40%, which will equate to between 4.0 and 5.0 volts. Depending on the charging issue, the PCM can drive the duty cycle to off (0%), which will equate to zero volts, or full field (100%), which will equate to between 11.0 and 12.0 volts.

      What is the Alternator duty cycle on the scan tool?

      0% 

      • Go To  3

      100% 

      • Go To  4
  3. CHECK THE (K20) ALTERNATOR FIELD CONTROL CIRCUIT FOR A SHORT TO VOLTAGE 
    1. Back probe the (K20) Alternator Field Control circuit at the Alternator harness connector.
      WARNING:

      When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

    2. Measure the voltage on the (K20) Alternator Field Control circuit at the Alternator harness connector.

      Is there any voltage present?

      Yes 

      • Repair the (K20) Alternator Field Control circuit for a short to voltage.
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .

      No 

      • Verify that there is good pin to terminal contact in the Alternator and Powertrain Control Module connectors. If no problems are found, replace the Alternator. Refer to GENERATOR, REMOVAL .
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  4. CHECK THE ALTERNATOR FIELD CONTROL CIRCUIT VOLTAGE 
    1. Back probe the (K20) Alternator Field Control circuit at the Alternator harness connector.
      WARNING:

      When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

    2. Measure the voltage on the (K20) Alternator Field Control circuit at the Alternator harness connector.

      Is the voltage between 11.0 and 12.0 volts?

      Yes 

      • Verify that there is good pin to terminal contact in the Alternator and Powertrain Control Module connectors. Also verify that engine block has a good ground and the Alternator has a good case ground. If no problem found, replace the Alternator. Refer to GENERATOR, REMOVAL .
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .

      No 

      • Go To  5
  5. CHECK THE (K20) ALTERNATOR FIELD CONTROL CIRCUIT FOR AN OPEN/HIGH RESISTANCE 
    1. Turn the ignition off.
    2. Disconnect the Alternator harness connector.
    3. Disconnect the PCM C2 harness connector.
      CAUTION:

      Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install the GPEC Diagnostic Adaptor to perform the diagnosis.

    4. Connect the (special tool #10436, Adapter, GPEC Diagnostic).
    5. Measure the resistance on the (K20) Alternator Field Control circuit between the Alternator harness connector and the GPEC Adaptor.

      Is the resistance below 3.0 Ohms?

      Yes 

      • Go To  6

      No 

      • Repair the (K20) Alternator Field Control circuit for an open or high resistance. Make sure to check for a spread terminal at the PCM harness connector.
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  6. CHECK THE (K20) ALTERNATOR FIELD CONTROL CIRCUIT FOR A SHORT TO GROUND 
    1. Check for continuity between ground and the (K20) Alternator Field Control circuit at the GPEC Adaptor.

      Is there continuity between ground and the (K20) Alternator Field Control circuit?

      Yes 

      • Repair the (K20) Alternator Field Control circuit for a short to ground.
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .

      No 

      • Go To  7
  7. CHECK RELATED PCM AND COMPONENT CONNECTIONS 
    1. Perform the NO RESPONSE FROM THE PCM test procedure to check the PCM powers and grounds. Refer to DIAGNOSIS AND TESTING .
    2. Perform any Service Bulletins that apply.
    3. Disconnect all PCM harness connectors.
    4. Disconnect all related in-line harness connections (if equipped).
    5. Disconnect the related component harness connectors.
    6. Inspect harness connectors, component connectors, and all male and female terminals for the following conditions:
      • Proper connector installation.
      • Damaged connector locks.
      • Corrosion.
      • Other signs of water intrusion.
      • Weather seal damage (if equipped).
      • Bent terminals.
      • Overheating due to a poor connection (terminal may be discolored due to excessive current draw).
      • Terminals that have been pushed back into the connector cavity.
      • Check for spread terminals and verify proper terminal tension.

      Repair any conditions that are found.

    7. Reconnect all PCM harness connectors. Be certain that all harness connectors are fully seated and the connector locks are fully engaged.
    8. Reconnect all in-line harness connectors (if equipped). Be certain that all connectors are fully seated and the connector locks are fully engaged.
    9. Reconnect all related component harness connectors. Be certain that all connectors are fully seated and the connector locks are fully engaged.
    10. With the scan tool, erase DTCs.
    11. Test drive or operate the vehicle in accordance with the when monitored and set conditions.
    12. With the scan tool, read DTCs.

      Did the DTC return?

      Yes 

      No 

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