The engine control module (ECM) 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 the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The ECM uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads.

The ECM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the ECM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 percent and 100 percent. The ECM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the ECM detects an out of range PWM signal, DTC P0622 will set.

DTC P0622 is a type C DTC.

DTC P0622 is a type C DTC.

Schematic Reference

Starting and Charging Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Charging System Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, engine OFF, observe the scan tool ECM GEN-F Terminal Signal parameter. The parameter should read 0%.
2. Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The parameter should read between 5 and 99%.

1. Verify that a test lamp illuminates between the B+ circuit terminal A X2 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

2. Ignition OFF, disconnect the X1 harness connectors at the generator and GBCM.
3. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter is 0%.

⇒	If greater than the specified value, test the field duty cycle signal circuit terminal 2 X1 for a short to voltage. If the circuit tests normal, replace the ECM.

4. Connect a test lamp between the field duty cycle signal circuit terminal 2 X1 of the generator harness and B+. Verify the scan tool ECM GEN-F Terminal Signal parameter is greater than 95%.

⇒	If less than the specified range, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

5. Reconnect the GBCM harness connector. Disconnect the test lamp.
6. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter is 0%.

⇒	If greater than the specified value, replace the GBCM.

7. Connect a test lamp between the field duty cycle circuit terminal 2 X1 of the generator harness and B+. Verify the scan tool ECM GEN-F Terminal Signal parameter is greater than 95%.

⇒	If less than the specified range, replace the GBCM.

8. If all circuits test normal, test or replace the generator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.