GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2008 🢒 H3 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC B1492

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

B+

B1492

B1492

--

--

Field Duty Cycle Signal

B1492

B1492

--

--

Turn On Signal

B1487

--

B1488

--

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 generator battery control module (GBCM) and the engine control module (ECM) monitor the generator through the generator field duty cycle signal circuit. The signal is a pulse width modulation (PWM) signal of 128 Hz. Normal duty cycle is 5-99 percent.

Conditions for Running the DTC
    • The engine is running.
    • The engine speed is less than 1,000 RPM.
    • DTC B1487 and DTC B1488 are not set.

Conditions for Setting the DTC

The generator field duty cycle signal 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 CHARGSYS message.

Conditions for Clearing the DTC
    • The generator field duty cycle signal is greater than 5 percent duty cycle.
    • The charge indicator and SERVICE CHARGSYS message will remain ON until the ignition switch is cycled after the DTC is cleared.

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. Ignition ON, engine OFF, observe the scan tool ECM GEN-F Terminal Signal parameter. The reading should be less than 5 percent.
    2. ⇒If greater than the specified range, refer to ECM Signal Circuit Malfunction.
  2. Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The reading should be greater than 5 percent.
    3. ⇒If less than the specified range, refer to ECM Signal Circuit Malfunction.
  3. Refer to GBCM Signal Circuit Malfunction.

Circuit/System Testing

ECM Signal Circuit Malfunction

  1. Verify that a test lamp illuminates between the B+ circuit ring terminal 1 X2 and ground.
    2. ⇒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, and the harness connector at the GBCM.
  3. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal is less than 5%.
    4. ⇒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 3A 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%.
    5. ⇒If less than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  5. Ignition OFF, Reconnect the harness connector at the GBCM. Remove the jumper wire from the generator harness connector.
  6. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal is less than 5%.
    7. ⇒If greater than the specified range, replace the GBCM.
  7. 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%.
    8. ⇒If less than the specified range, replace the GBCM.
  8. If all circuits test normal, test or replace the generator.

GBCM Signal Circuit Malfunction

  1. Ignition OFF, disconnect the harness connector at the GBCM.
  2. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal is less than 5%.
    3. ⇒If greater than the specified range, test the signal circuit terminal B for a short to voltage.
  3. Install a 3A fused jumper wire between the signal circuit terminal B and B+. Verify the scan tool ECM GEN-F Terminal Signal is greater than 95%.
    4. ⇒If less than the specified range, test the signal circuit for a short to ground or an open/high resistance.
  4. If all circuits test normal, replace the GBCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Generator Replacement
    •  Control Module References for ECM or GBCM replacement, setup, and programming.