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DTC B3887 or B3888 (With U4G)

DTC B3887 or B3888 (With U4G)

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 B3887 02

Trailer Left Turn Signal Circuit Short to Ground

DTC B3887 04

Trailer Left Turn Signal Circuit Open

DTC B3888 02

Trailer Right Turn Signal Circuit Short to Ground

DTC B3888 04

Trailer Right Turn Signal Circuit Open

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Trailer Left Turn Signal B3887 02 B3887 04 1 -
Trailer Right Turn Signal B3888 02 B3888 04 2 -
1. Left Trailer Turn Signal Lamp Always On 2. Right Trailer Turn Signal Lamp Always On


Circuit/System Description

The trailer brake control module will receive a serial data message from the BCM indicating that the vehicle left turn signal lamp or the right turn signal lamp has been activated. The trailer brake control module will then apply a pulsating voltage to the appropriate trailer turn signal lamps through their respective voltage supply circuits.

Conditions for Running the DTC

When the trailer left turn lamp or right turn lamp is being actively commanded by the trailer brake control module.

Conditions for Setting the DTC

B3887 02 or B3888 02

The trailer brake control module detects a short to ground on the appropriate turn signal control circuit.

B3887 04 or B3888 04

The trailer brake control module detects an open/ high resistance in the appropriate turn signal control circuit.

Action Taken When the DTC Sets

The appropriate trailer turn signal lamp will be inoperative.

Conditions for Clearing the DTC


The DTC will be current for as long as the fault is present.

When the fault is no longer present, the DTC will be a history DTC.

A history DTC will clear after 40 ignition cycles.


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


Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, observe the function of the left trailer turn signal lamp and the right trailer turn signal lamp while commanding the Left Trailer Turn Signal Lamp and the Right Trailer Turn Signal Lamp ON and OFF with a scan tool. The left trailer turn signal lamp and the right trailer turn signal lamp 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.

2. Test for infinite resistance between the control circuit terminal listed below and ground:

Right trailer turn signal lamp control terminal 2

Left trailer turn signal lamp control terminal 17

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.

4. Test for less than 1 Ω between the control circuit terminals listed below:

Control terminal 2 at the K68 trailer lighting control module and control terminal 4 at the X88 trailer connector.

Control terminal 17 at the K68 trailer lighting control module and control terminal 1 at the X88 trailer connector.

5. If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance.

6. If all the circuits test normal, replace the K68 trailer lighting control module.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for trailer brake control module replacement, programming and setup