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 Circuit Low VoltageCircuit/System Description
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 key ON test and a RUN test. During the tests, if the ECM detects an out of range PWM signal, a DTC will set.
Conditions for Running the DTC
| • | The vehicle speed is above 8 km/h (5 mph). |
| • | The engine speed is less than 3,000 RPM. |
Conditions for Setting the DTC
The ECM detects a pulse width modulated (PWM) signal less than 5 percent for at least 15 seconds.
Action Taken When the DTC Sets
| • | The ECM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC), if equipped. |
| • | The ECM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM will store conditions, which were present when the DTC set as Failure Records data only. |
Conditions for Clearing the DTC
| • | The ECM will command the message OFF after one trip in which the diagnostic test has been run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
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
Scan Tool Reference
Circuit/System Verification
Engine running, observe the scan tool GEN-F Terminal Signal parameter. The GEN-F Terminal Signal parameter should read between 5-95 percent.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the generator.
- Ignition ON, engine OFF, observe the scan tool GEN-F Terminal Signal parameter, while repeatedly probing the generator field duty cycle circuit with a test lamp connected to battery positive voltage. The parameter should change from 0 percent to above 95 percent.
| ⇒ | If the parameter was not affected by the test lamp, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. |
If the circuit tested normal and the ECM parameter changed from 0 percent to above 95 percent, replace the generator.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM replacement, setup, and programming
Generator Replacement for generator replacement.
