GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 Canyon Pickup - 4WD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 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

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.
    2. ⇒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.
    3. ⇒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.
    3. ⇒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.
    4. ⇒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.
    6. ⇒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.
    7. ⇒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.
    3. ⇒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.
    4. ⇒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.