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Trailer Lamps Malfunction





Trailer Lamps Malfunction

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.

Diagnostic Fault Information






Circuit/System Description

The vehicle's trailer lighting control system contains an auxiliary body control module (XBCM) to send lighting commands to the trailer lighting system. The vehicle's trailer wiring harness and XBCM is integrated into the vehicle wiring harness and controls the signals to the trailer connector. Battery voltage is supplied to the XBCM from the REAR/FOG/XBCM fuse located in the rear fuse block.

Reference Information

Schematic Reference

Trailer Connector/Provision Schematics Trailer Connector/Provision Schematics

Connector End View Reference

Component Connector End Views A/C Compressor Clutch

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 Control Module References for scan tool information

Circuit/System Testing

Trailer Brake Lamp Circuit Malfunction

1. Ignition OFF, test for less than 1 ohms between the appropriate trailer connector ground circuit terminal and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

2. Connect a test lamp between the appropriate trailer connector control circuit terminal and ground.

3. Press and release the brake pedal, the test lamp should illuminate each time the brake pedal is pressed.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the auxiliary fuse block.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the auxiliary fuse block.

4. If all circuits test normal, replace the auxiliary fuse block.

Trailer Backup Lamp Circuit Malfunction

1. Ignition OFF, disconnect the X1 harness connector at the auxiliary BCM.

2. Test for less than 1 ohms between the low reference circuit terminal A1 and circuit terminal B7.

• If greater than the specified range, test the low reference terminal for a short to voltage or an open/high resistance.

3. Connect a test lamp between the control circuit terminal B1 and ground.

4. Command the Backup Lamps ON and OFF with a scan tool, the test lamp should turn ON and OFF while changing between the commanded states.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

• If the test lamp is always ON, test the control circuit for a short to voltage.

5. Ignition OFF, connect the X1 harness connector and disconnect the X2 harness connector at the XBCM.

6. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal B and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

7. Ignition OFF, connect the X2 harness connector at the XBCM.

8. Connect a test lamp between the appropriate trailer connector circuit terminal and ground.

9. Ignition ON, command the Backup Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF while 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 XBCM.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the XBCM.

10. If all circuits test normal, replace the XBCM.

Trailer Turn Signal Circuit Malfunction

1. Ignition OFF, disconnect the appropriate Trailer Turn relay.

2. Test for less than 1.0 ohms between the ground circuit terminal A1 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 and ground.

• If the test lamp illuminates, test the control circuit for a short to voltage.

4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Ignition ON, connect a 15 A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify that a test lamp illuminates between the appropriate trailer connector terminal and ground.

• If the test lamp does not illuminate, test the control circuit for an open/high resistance.

6. Connect a test lamp between the control circuit terminal C2 and the ground circuit terminal A1.

7. Command the LR Turn Signal or RR Turn Signal 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 control circuit for a short to voltage.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

8. If all circuits test normal, test or replace the Trailer Turn relay.

Trailer Parking Lamp Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the auxiliary fuse block

2. Connect a test lamp between the control circuit terminal A and ground.

3. Ignition ON, command the Parking Lamps ON and OFF with a scan tool, the test lamp should turn ON and OFF while changing between the commanded states.

• If the test lamp is always ON, test the control circuit for a short to voltage.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance.

4. Connect a 7.5 A fused jumper wire between the control circuit terminal B and B+. Verify that a test lamp illuminates between the appropriate trailer connector control circuit terminal and ground.

• If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

5. If all circuits test normal, replace the auxiliary fuse block.

Trailer Fog Lamp Circuit Malfunction

1. Ignition OFF, disconnect the X2 harness connector at the XBCM.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal B and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the X2 harness connector at the XBCM.

4. Connect a test lamp between the appropriate trailer connector control circuit terminal and ground.

5. Ignition ON, command the Trailer Fog Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF while 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 XBCM.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the XBCM.

6. If all circuits test normal, replace the XBCM.

Component Testing

Relay Test

1. Ignition OFF, disconnect the appropriate relay.

2. Test for 60-200 ohms between terminals 85 and 86.

• If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86

* 30 and 86

* 30 and 86

* 30 and 86

• If less than the specified value, replace the relay.

4. Test for less than 2 ohms between terminals 30 and 87 A.

• If greater than the specified range, replace the relay.

5. Install a 3 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

• If greater than specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Underhood Electrical Center or Junction Block Replacement Underhood Electrical Center or Junction Block Replacement

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Control Module References Control Module References for BCM replacement, setup, and programming

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