B3890
DTC B3890
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 Descriptor
DTC B3890 02
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Trailer Backup Lamps Circuit Short to Ground
Diagnostic Fault Information
Circuit/System Description
When the transmission is placed in the reverse position, the engine control module (ECM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the reverse position. The BCM then applies a voltage to the trailer backup lamps through their supply circuit.
Conditions for Running the DTC
The appropriate trailer backup lamp signal is active.
Conditions for Setting the DTC
The BCM detects a short to ground on the control circuit.
Conditions for Clearing the DTC
The condition for setting the DTC is no longer present.
Action Taken When the DTC Sets
The appropriate trailer backup lamp is inoperative.
Reference Information
Schematic Reference
Trailer Connector/Provision Schematics Trailer Connector/Provision Schematics
Connector End View Reference
Component Connector End Views Sunshade - Left Front
Description and Operation
Exterior Lighting Systems Description and Operation Exterior Lighting Systems
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 Programming and Relearning for scan tool information
Circuit/System Verification
Engine running, shift the transmission into and out of the reverse position. The trailer backup lamps should turn ON and OFF when shifting between the commanded states.
Circuit/System Testing
1. Ignition OFF, disconnect the X2 harness connector at the X50A underhood fuse block.
2. Connect a test lamp between the control circuit terminal K1 and B+.
3. Turn the headlamp switch between the OFF and park light positions. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace K9 BCM.
4. Ignition OFF, connect the X2 harness connector at the X50A underhood fuse block.
5. Test for less than 5 ohms between the X88 Trailer Connector ground circuit terminal D and ground
• If greater than the specified range, test the ground circuit for an open/high resistance.
6. Connect a test lamp between the control circuit terminal B and ground.
7. Turn the headlamp switch between the OFF and park light positions. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the X88 Trailer Connector.
• If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the X88 Trailer Connector.
• If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the X88 Trailer Connector.
8. If all circuits test normal, test or replace the X50A underhood fuse block.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Accessory Wiring Junction Block Replacement Accessory Wiring Junction Block Replacement
* Control Module References Programming and Relearning for trailer lighting converter replacement, setup and programming