B3891
DTC B3891
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 Descriptors
DTC B3891 02
-
Trailer Fog Lamps Circuit Short to Ground
DTC B3891 05
-
Trailer Fog Lamps Circuit Short to Battery or Open
Diagnostic Fault Information
Circuit/System Description
When the rear fog lamp switch is placed in the ON position, ground is applied to the auxiliary body control module (XBCM) through the rear fog lamp switch circuit. The XBCM then applies voltage on the trailer fog lamp circuit to the trailer rear fog lamp.
Conditions for Running the DTC
The ignition is ON. Park lamps must be ON and the rear fog lamps must be commanded ON.
Conditions for Setting the DTC
B3891 02
The XBCM detects a short to ground on the trailer fog lamp control circuit.
B3891 05
The XBCM detects a short to voltage or an open circuit on the trailer fog lamp control circuit.
Action Taken When the DTC Sets
The trailer fog lamps do not illuminate.
Conditions for Clearing the DTC
* The conditions for setting the DTC are no longer present.
* A history DTC clears after 100 malfunction-free ignition cycles.
* The BCM receives the clear code command from the scan tool.
Reference Information
Schematic Reference
Trailer Connector/Provision Schematics Trailer Connector/Provision Schematics
Connector End View Reference
Component Connector End Views A/C Compressor Clutch
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
Ignition ON, command the Trailer Fog Lamps ON and OFF with a scan tool. The trailer fog lamps should turn ON and OFF as commanded.
Circuit/System Testing
1. Inspect the trailer rear fog lamp bulb for an open or shorted filament.
• If the bulb is inoperable, replace the bulb.
2. Park lamp switch OFF, clear the DTC. Test the trailer rear fog lamp circuit for a short to voltage, short to ground, an open, or high resistance.
• If all circuits/connections test normal, replace the XBCM.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
Control Module References Control Module References for XBCM replacement, setup, and programming