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 Circuit Low Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
B+ | P0625 | P0625 | -- | --
Field Duty Cycle Signal | P0625 | P0625 | P0626 | --
Turn On Signal | P0621 | -- | P0621 | --

### Typical Scan Tool Data

#### GEN F-Terminal Signal - ECM

Circuit | Short to ground | Open | Short to voltage
--- | --- | --- | ---
Operating Conditions: Engine Running Parameter Normal Range: 5% to 99%
B+ | 0% | 0% | --
Field Duty Cycle Signal | 0% | 0% | 99%

### Circuit/System Description

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 high side of the field windings in the generator. 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 generator 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 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. When the engine is running, the duty cycle should be between 5-99 percent.

### Conditions for Running the DTC

• | The vehicle speed is greater than 8 km/h (5 mph).

• | The engine speed is less than 3,000 RPM.

### Conditions for Setting the DTC

The ECM detects that the field duty cycle signal is less than 5 percent for 15 seconds.

### Action Taken When the DTC Sets

• | The charge indicator turns ON.

• | The driver information center (DIC) will display the SERVICE BATTERY CHARGING SYSTEM message.

• | The ECM will not illuminate the malfunction indicator lamp (MIL).

• | The ECM will store conditions, which were present when the DTC set as Fail Records data only.

### Conditions for Clearing the DTC

• | The DTC passes when condition for setting the DTC is no longer present.

• | 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

Component Connector End Views

#### Description and Operation

Charging System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, engine OFF, observe the scan tool ECM GEN-F Terminal Signal parameter. The reading should be less than 5 percent.
2. Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The reading should be greater than 5 percent.

### Circuit/System Testing

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

⇒ | 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 3 A fused jumper wire between the signal circuit terminal 2 X1 and B+. Verify the scan tool ECM GEN-F Terminal Signal is greater than 95%.

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

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Generator Replacement

• | Control Module References for ECM replacement, setup, and programming.