PRE-RELEASE
DTC B3891
| DTC B3891 |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
provides an overview of each diagnostic category.
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| DTC Descriptors |
DTC B3891 02
Trailer Fog Lamps Circuit Short to Ground
DTC 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 Control | B3891 02 | B3891 04 | 1 | - |
| 1. Trailer Fog Lamps Always ON | ||||
| Circuit/System Description |
The trailer brake control module will receive a serial data message from the BCM indicating that the vehicle rear fog lamps have been activated. The trailer brake control module will then apply system voltage to the trailer fog lamps through their respective voltage supply circuits.
| Conditions for Running the DTC |
When the trailer fog lamps are turned on.
| Conditions for Setting the DTC |
B3891 02
The trailer brake control module detects a short to ground on the trailer fog lamp control circuit.B3891 04
The trailer brake control module detects an open/high resistance on the trailer fog lamp control circuit.| Action Taken When the DTC Sets |
The trailer fog lamps will be inoperative.
| Conditions for Clearing the DTC |
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The DTC will be current for as long as the fault is present.
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When the fault is no longer present, the DTC will be a history DTC.
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A history DTC will clear after 40 ignition cycles.
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| Reference Information |
Schematic Reference
Trailer Connector/Provision Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
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Circuit Testing
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Connector Repairs
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Testing for Intermittent Conditions and Poor Connections
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Wiring Repairs
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Scan Tool Reference
Control Module References for scan tool information
| Circuit/System Verification |
Ignition ON, observe the function of the trailer fog lamps while commanding the Trailer Fog Lamp ON and OFF with a scan tool. The trailer fog lamps should turn ON and OFF while changing between the commanded states.
| Circuit/System Testing |
| 1. |
Ignition OFF, disconnect the X1 harness connector at the K68 trailer lighting control module.
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| 2. |
Test for infinite resistance between the control circuit terminal 8 and ground.
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| 3. |
If less than the specified value, test the control circuit for a short to ground. If the circuit tests normal, replace the X88 trailer connector.
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| 4. |
Test for less than 1 Ω between the control circuit terminal 8 at the K68 trailer lighting control module and control circuit terminal 2 at the X88 trailer connector.
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If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the X88 trailer connector.
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If all the circuits test normal, replace the K68 trailer lighting control module.
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| Repair Instructions |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for trailer brake control module replacement, programming and setup
