Diagnostic Instructions

1. Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
2. Review Strategy Based Diagnosis for an overview of the diagnostic approach.
3. Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

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	3887 02	3887 04	--	--
Trailer Right Turn Signal	B3888 02	B3888 04	--	--

Circuit/System Description

Ground is applied at all times to the turn signal/multifunction switch. When the turn signal/multifunction switch is placed in either the turn right or turn left position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM sends this message to the trailer lighting converter. The trailer lighting converter then applies a voltage to the appropriate trailer turn signal lamps through there respective voltage supply circuits.

Conditions for Running the DTC

B3887 02, B3887 04, B3888 02 and B3888 04

The appropriate trailer turn signal is active

Conditions for Setting the DTC

B3887 02 or B3888 02

The trailer lighting converter detects a short to ground on the control circuit.

B3887 04 or B3888 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 turn signal lamp is inoperative.

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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, perform the appropriate Trailer Turn Signal Lamp test. The appropriate trailer turn signal lamp should be ON/OFF

Circuit/System Testing

1. Ignition OFF, test for less than 5 Ω between the X88 Trailer Connector terminal 3, 11, 13 and ground.

⇒	If greater than the specified value, test the appropriate ground circuit for an open/high resistance.

2. Connect a test lamp between the appropriate X88 Trailer Connector terminal listed below and ground.

•	X88 Trailer Connector terminal 1

•	X88 Trailer Connector terminal 4

3. Command the appropriate Trailer Turn Signal Lamp Active / Inactive test with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	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.

4. If all the circuits test normal, test the appropriate turn signal lamp circuit at the trailer.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for trailer lighting converter replacement, setup and programming