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

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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