For 1990-2009 cars

### 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 Voltage
DTC P0626: Generator F Terminal High Voltage

### Circuit/System Description

The engine control module (ECM) uses the alternator field duty cycle signal circuit to monitor the duty cycle of the alternator. The alternator field 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 field 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 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. 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 MIL/DTC

DTC's P0625 and P0626 are type C Store Only DTCs

### Reference Information

#### Schematic Reference

Starting and Charging Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References

### 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

1. Ignition OFF, disconnect the alternator harness connector.
2. 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.

Control Module References