Diagnostic Instructions
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
DTC Descriptor
DTC B1492: Generator F-Terminal Circuit LowDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
B+ | B1492 | B1492 | -- | -- |
Field Duty Cycle Signal | B1492 | B1492 | -- | -- |
Charge Indicator Control | B1487 | -- | B1488 | -- |
Circuit/System Description
The generator battery control module (GBCM) monitors the generator through the field duty cycle signal circuit, or F-Terminal circuit. The signal is pulse width modulated (PWM) by the generator. The normal duty cycle with the engine running is 5-99 percent.
Conditions for Running the DTC
| • | DTC B1487 or B1488 are not set. |
| • | The engine is running. |
| • | The engine speed is less than 1,000 RPM. |
Conditions for Setting the DTC
The GBCM detects that the field duty cycle signal is less than 5 percent for 2 minutes.
Action Taken When the DTC Sets
| • | The charge indicator turns ON. |
| • | The driver information center (DIC) displays the SERVICE CHARGING SYSTEM message. |
Conditions for Clearing the DTC
| • | The DTC will pass when the field duty cycle signal is greater than 5 percent. |
| • | The charge indicator and the DIC message will remain ON until the next ignition cycle. |
Diagnostic Aids
Do not use the ECM GEN F-Terminal scan tool parameter on light-duty vehicles built after mid-year 2005. The ECM does not monitor the field duty cycle signal circuit on these vehicles.
Reference Information
Schematic Reference
Starting and Charging Schematics
Connector End View Reference
Engine Electrical Connector End Views
Description and Operation
Charging System Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Verify that a test lamp illuminates between the B+ circuit ring terminal and ground.
- Ignition OFF, disconnect the harness connector at the GBCM.
- Engine running, test for 5-99 percent duty cycle on the signal circuit terminal B.
- If all circuits test normal, replace the GBCM.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
| ⇒ | If not within the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the generator. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for GBCM replacement, setup, and programming. |
