Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P0625: Generator F Terminal Low VoltageDTC P0626: : Generator F Terminal high Voltage
Circuit/System Description
The engine control module (ECM) uses the alternator ?eld duty cycle signal circuit to monitor the duty cycle of the alternator. The alternator ?eld duty cycle signal circuit connects to high side of the field windings in the alternator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the ?eld windings ON and OFF. The ECM uses the PWM signal input to determine the alternator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM monitors the status of the alternator ?eld 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. When the engine is running, the duty cycle should be between 5-95 percent.
Conditions for Running the DTC
| • | The vehicle speed is above 8 km/h (5 mph). |
| • | The system voltage is between 9.5-18 volts. |
Conditions for Setting the DTC
With the engine running, the ECM detects a PWM signal less than 5 percent for at least 15 seconds.
Action Taken When the DTC Sets
DTC’s P0625 and P0626 are type C Store Only DTCs
Conditions for Clearing the DTC
DTC’s P0625 and P0626 are type C Store Only DTCs
Reference Information
Schematic Reference
Starting and Charging Schematics
Connector End View Reference
Engine Electrical Connector End Views
Description and Operation
Charging System Description and Operation
Electrical Information Reference
Circuit/System Verification
With the scan tool installed, ignition ON and the engine running, observe the alternator F Terminal Signal parameter in the ECM data list. The alternator F Terminal Signal parameter should read between 5 and 95 percent.
Circuit/System Testing
- Ignition OFF
- Disconnect the alternator harness connector.
- With the ignition ON, engine OFF, connect a test lamp to battery positive voltage and repeatedly probe the alternator field duty cycle circuit, harness side while monitoring the alternator-F Terminal Signal Parameter in the ECM data list, it should change from 0 percent to above 95 percent.
- If the alternator-F Terminal Signal parameter was not affected by the test lamp, test the alternator- F Terminal Signal circuit for a short to ground or an open/high resistance. If circuit tests normal replace the ECM.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
