The engine control module (ECM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator and fault indication. 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 engine is running, the ECM should detect a duty cycle that varies up to 100 percent. The ECM monitors the PWM signal using a Ignition ON test and a RUN test. During the tests, if the ECM detects an out of range PWM signal, a DTC will set.

The ECM detects a pulse width modulated (PWM) signal greater than 65 percent for 15 seconds.

DTC P0626 is a C type 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

Ignition ON, engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The GEN-F Terminal Signal parameter should read between 5-95 percent.

1. Verify that a test lamp illuminates between the generator output B+ circuit terminal B 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 harness connector X1 at the generator.
3. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter displays less than 5 percent.

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

4. Install a 3A fused jumper wire between B+ and the signal circuit.
5. Verify the scan tool ECM GEN-F Terminal Signal parameter displays greater than 95 percent.

⇒	If less than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

6. If the circuit tests normal replace the generator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.