B1492
DTC B1492
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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) 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 ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector 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 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 (Verification Tests) after completing the diagnostic procedure.
* Generator Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for GBCM replacement, setup, and programming.