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 B1492: Generator F-Terminal Circuit Low

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Generator Field Duty Cycle Signal | B1492 | B1492 | -- | --

### 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%
Generator Field Duty Cycle Signal | 0% | 0% | 99%

### Circuit/System Description

The generator battery control module (GBCM) monitors the generator through the generator field duty cycle signal circuit. The signal is a pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent when the engine is running. If the generator field duty cycle signal circuit is in the 0-5 percent range or pulled low to ground while the engine is running, then DTC B1492 will set.

### Conditions for Running the DTC

• | The engine is running.

• | The engine speed is less than 1,000 RPM.

• | DTC B1487 or B1488 is not set as a current DTC.

• | This diagnostic shall be run every 100 ms.

### Conditions for Setting the DTC

The generator field duty cycle signal circuit is less than 5 percent duty cycle for 2 minutes.

### Action Taken When the DTC Sets

• | The charge indicator turns ON.

• | The driver information center (DIC) displays the SERVICE CHARGE SYS message.

### Conditions for Clearing the DTC

• | The DTC passes when the generator field duty cycle signal circuit input is greater than 5 percent duty cycle.

• | You must cycle the ignition after clearing the DTC to turn OFF the indicator and DIC message .

### 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

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The parameter should read greater than 5 percent.

⇒ | If not within the specified range, refer to ECM Field Duty Cycle Signal Circuit Malfunction.

2. Verify that the GBCM does not set DTC B1492.

⇒ | If the GBCM sets DTC B1492, refer to GBCM Field Duty Cycle Signal Circuit Malfunction.

### Circuit/System Testing

#### ECM Field Duty Cycle Signal Circuit Malfunction

1. Ignition OFF, disconnect the X1 harness connectors at the generator and GBCM.
2. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter is 0 percent.

⇒ | If greater than the specified value, test the field duty cycle signal circuit terminal 2 X1 for a short to voltage. If the circuit tests normal, replace the ECM.

3. Connect a test lamp between the field duty cycle signal circuit terminal 2 X1 of the generator harness and B+. Verify the scan tool ECM GEN-F Terminal Signal parameter is greater than 95 percent.

⇒ | If less than the specified range, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Reconnect the GBCM harness connector. Disconnect the test lamp.
5. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter is 0 percent.

⇒ | If greater than the specified value, replace the GBCM.

6. Connect a test lamp between the field duty cycle circuit terminal 2 X1 of the generator harness and B+. Verify the scan tool ECM GEN-F Terminal Signal parameter is greater than 95 percent.

⇒ | If less than the specified range, replace the GBCM.

7. If the circuit tests normal, replace the generator.

#### GBCM Field Duty Cycle Signal Circuit Malfunction

1. Ignition OFF, disconnect the GBCM harness connector.
2. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter is 0 percent.

⇒ | If greater than the specified value, test the field duty cycle signal circuit terminal B for a short to voltage.

3. Connect a test lamp between the field duty cycle signal circuit terminal B and B+. Verify the scan tool ECM GEN-F Terminal Signal parameter is greater than 95 percent.

⇒ | If less than the specified range, test the circuit for a short to ground or an open/high resistance.

4. If the circuit tests normal, replace the GBCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Generator Replacement

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