P0622 Generator Field Control Circuit

P0622 Code - The Powertrain Control Module (PCM) uses the Generator field duty cycle signal circuit or F-terminal circuit, to monitor the duty cycle of the generator. The Generator field duty cycle signal circuit connects to high side of the field windings in the Generator.




 A pulse widht modulated (PWM) high side driver in the voltage regulator turns the field windings ON and OFF. The PCM uses the PWM signal input to determine the generator load on the engine. This allow the PCM to adjust the idle speed to compensate for high electrical loads. The PCM monitors the status of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-95 percent.
Set condition, the Powertrain Control Module (PCM) attempts to regulate the Alternator field with no result during monitoring. Default actions is non MIL fault, if the vehicle is equipped with the stop/start feature, the system will be disabled when this DTC is active.

Possible cause P0622 Code

  • Alternator field control circuit shorted to battery voltage
  • Alternator field control circuit open/high resistance
  • Alternator field control circuit shorted to ground
  • Poor engine block or alternator case ground
  • Alternator
  • Powertrain Control Module (PCM)

Diagnose P0622 Code


Step 1. Check for an active DTC
Start the engine and allow it to idle
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.
With the scan tool, read DTCs.

Is the DTC active or pending at this time?

Yes, go to step 2.
No, perform the PCM intermittent condition.

Step 2. Check the Alternator duty cycle
With the scan tool, cehck the duty cycle reading for the alternator. 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 step 3.
100% , go to step 4.

Step 3. Check the Alternator field control circuit for a short to voltage
Back probe the Alternator field control circuit at the Alternator harness connector. measure the voltage between ground nd the Alternator field control circuit at the Alternator harness connector.

Is there any voltage present?

Yes, repair the Alternator field control circuit for a short to voltage.
No, Verify that there is good pin to terminal contact in  the Powertrain Control Module (PCM) connectors. If no problems are found, replace the Alternator.

Step 4. Check the Alternator field control circuit voltage
Back probe the Alternator field control circuit at the Alternator harness connector. Measure the voltage between ground and the 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 (PCM) connectors. Also verify that engine block has a good ground and the Aternator has a good case ground. If Ok, replace the Alternator.

No, go to step 5.

Step 5. Check the Alternator field control circuit for an open/high reistance
Turn the ignition off, disconnect the Alternator harness connector. Disconnect the PCM harness connector, measure the resistance on the Alternator field control circuit between the Alternator harness connector and the PCM harness connector.

Is the resistance below 3.0 Ohms?

Yes, go to step 6.
No, repair the Alternator field control circuit for an open or high resistance, make sure to check for a spread terminal at the PCM harness connector.

Step 6. Check the Alternator field control circuit for a short to ground
Check for continuity between ground and the Alternator field control circuit at the PCM harness connector.

Is there continuity between ground and the Alternator field control circuit?

Yes, repair the Alternator field control circuit for a short to ground.
No, go to step 7.

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