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






Typical Scan Tool Data






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 with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. 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 the GBCM will set DTC B1492.


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.



Conditions for Setting the DTC

The generator field duty cycle signal circuit is less than or equal to 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 circuit input is greater than 5 percent duty cycle.
* The charge indicator and the SERVICE CHARGSYS message will remain ON until the next ignition cycle.



Reference Information
Schematic Reference

Starting and Charging Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Component Connector End Views)
Description and Operation

Charging System Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Verification

1. Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The parameter should read between 5 and 99 percent.

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




Circuit/System Testing


ECM Generator Field Duty Cycle Signal Circuit Malfunction
1. Ignition OFF, disconnect the harness connectors at the generator and GBCM.
2. Ignition ON, engine OFF, connect a test lamp to B+ and repeatedly probe the generator field duty cycle circuit terminal 2 of the generator while monitoring the ECM GEN-F Terminal Signal parameter. The parameter should change from less than 5 percent to greater than 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. If the circuit tests normal, replace the ECM.

3. Reconnect the harness connector at the GBCM.
4. Repeatedly probe the generator field duty cycle circuit terminal 2 of the generator with the test lamp that is connected to B+, harness side while monitoring the ECM GEN-F Terminal Signal parameter. It should change from less than 5 percent to greater than 95 percent.

• If the parameter was not affected by the test lamp, replace the GBCM.

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



GBCM Generator Field Duty Cycle Signal Circuit Malfunction
1. Ignition OFF, disconnect the harness connector at the GBCM.
2. Ignition ON, engine OFF, connect a test lamp to B+ and repeatedly probe the generator field duty cycle circuit terminal B of the GBCM while monitoring the ECM GEN-F Terminal Signal parameter. The parameter should change from less than 5 percent to greater than 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.

* Generator Replacement (LH8) (Generator Replacement)Generator Replacement (LLR) (Generator Replacement)
* Control Module References (Programming and Relearning) for ECM or GBCM replacement, setup, and programming