Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC B3891 02: Trailer Fog Lamps Circuit Short to GroundDTC B3891 04: Trailer Fog Lamps Circuit Open
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Trailer Fog Lamps | 3891 02 | 3891 04 | -- | -- |
Circuit/System Description
The front fog lamp switch signal circuit is grounded momentarily by pressing the front fog lamp switch. The body control module (BCM) sends this message to the trailer lighting converter. The trailer lighting converter then applies a voltage to the trailer fog lamps through there supply circuit.
Conditions for Running the DTC
B3891 02 or B3891 04
The appropriate trailer fog lamps signal is active
Conditions for Setting the DTC
B3891 02
The trailer lighting converter detects a short to ground on the control circuit.
B3891 04
The trailer lighting converter detects an open control circuit.
Conditions for Clearing the DTC
The condition for setting the DTC is not longer present.
Action Taken When the DTC Sets
The appropriate trailer fog lamp is inoperative.
Reference Information
Schematic Reference
Trailer Connector/Provision Schematics
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Ignition ON, perform the Trailer Fog Lamp(s) test. The trailer fog lamps should be ON/OFF
Circuit/System Testing
- Ignition OFF, test for less than 5 Ω between the X88 Trailer Connector terminal 3, 11, 13 and ground.
- Connect a test lamp between the X88 Trailer Connector terminal 2 and ground.
- Command the Trailer Fog Lamp(s) Active / Inactive test with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all the circuits test normal, test the fog lamps circuit at the trailer.
| ⇒ | If greater than the specified value, test the appropriate ground circuit for an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K68 Trailer Lighting Converter. |
| ⇒ | If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the K68 Trailer Lighting Converter. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for trailer lighting converter replacement, setup and programming
