B1492

DTC B1492

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC B1492
^ Generator F-Terminal Circuit Low

Diagnostic Fault Information





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 5-95 percent. If the generator field duty cycle signal circuit is in the 0-5 percent range or pulled low to ground, then DTC B1492 will set.

Conditions for Running the DTC

* Vehicle in RUN mode and Engine Run Flag is True.
* The engine speed is less that 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 or equal to 5 percent duty cycle for more than 120 seconds.

Action Taken When the DTC Sets

* The charge indicator turns ON.
* The driver information center (DIC) displays the BATTERY message.

Conditions for Clearing the DTC

The generator field duty cycle signal circuit input is greater than 5 percent duty cycle.

Diagnostic Aids

You must cycle the ignition after clearing the DTC to turn OFF the BATTERY 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 (Description and Operation)

Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Verification

With the scan tool installed, ignition ON and the Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The parameter should read between 5 and 95 percent.

Circuit/System Testing

1. Ignition OFF, disconnect the generator and GBCM harness connectors.
2. Ignition ON and engine OFF, connect a test lamp to B+ and repeatedly probe the generator field duty cycle circuit X1 - 2, harness side while monitoring the GEN-F Terminal Signal Parameter. It should change from 0 percent to above 95 percent.

• If the parameter was not affected by the test lamp, test the circuit for a short to voltage, short to ground, or an open/high resistance.

3. If the circuit tests normal, replace the GBCM

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Control Module References (Control Module References) for GBCM replacement, setup, and programming
* Generator Replacement (With 4.2L Engine) ()Generator Replacement (5.3L Engine) (Generator Replacement (5.3L Engine))