For 1990-2009 cars

### 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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Trailer Box Converter Module B+ | 1 | 1 | -- | --
Backup Lamps Signal | 1 | 1 | 1 | --
Park Lamps Signal | 1 | 1 | 1 | --
Stop Lamps Signal | 1 | 1 | 1 | --
Turn Signal Lamps Signal - Left | 1 | 1 | 1 | --
Turn Signal Lamps Signal - Right | 1 | 1 | 1 | --
Backup Lamps Control | 1 | 1 | 1 | --
Park Lamps Control | 1 | 1 | 1 | --
Stop Lamps Control | 1 | 1 | 1 | --
Turn Signal Lamps Control - Left | 1 | 1 | 1 | --
Turn Signal Lamps Control - Right | 1 | 1 | 1 | --
Trailer Box Converter Module Ground | -- | 1 | -- | --
Trailer Connector Ground | -- | 1 | -- | --
1. Trailer Lamps Malfunction

### Circuit/System Description

The trailer harness contains an electronic control unit (ECU) to control the lighting signals to the trailer lamps. The trailer harness and trailer ECU is integrated into the vehicle wiring harness and controls the signals to the standard 7-pin trailer connector. The trailer connector is mounted to the vehicles rear fascia. Battery Voltage is supplied to the trailer ECU from the 30 A Trailer fuse located in the rear fuse block. The trailer harness also provides a connection for the addition of an electronic trailer brake system.

### 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

1. Ignition ON, command the Reverse Light Test On and Off with a scan tool. The vehicles backup lamps should turn on and off when commanded.

⇒ | If the backup lamps do not turn On and Off when commanded, refer to Backup Lamps Malfunction.

2. Command the Parking Light Test On and OFF with a scan tool. The vehicles park lamps should turn on and off when commanded.

⇒ | If the park lamps do not turn On and Off when commanded, refer to Park, License, and/or Tail Lamps Malfunction.

3. Command the Brake Light Test On and OFF with a scan tool. The vehicles stop lamps should turn on and off when commanded.

⇒ | If the stop lamps do not turn on and off when commanded, refer to Stop Lamps Malfunction.

4. Command the Rear Turn Signal Test On and OFF with a scan tool. The vehicles stop lamps should turn on and off when commanded.

⇒ | If the rear turn signal lamps do not turn on and off when commanded, refer to Turn Signal Lamps and/or Indicators Malfunction.

5. Verify the trailer lamps operate properly. All trailer lamps should illuminate when commanded.

⇒ | If all trailer lamps are inoperative, refer to Trailer Lamps Malfunction - All

⇒ | If individual trailer lamps are inoperative, refer to Trailer Lamps Malfunction - Individual

### Circuit/System Testing

#### Trailer Lamps Malfunction - All

1. Ignition OFF, disconnect the harness connector at the trailer box converter module.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 3 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 illuminates between the B+ circuit terminal 6 and ground.

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

4. If all circuits test normal, replace the trailer box converter module.

#### Trailer Lamps Malfunction - Individual

1. Ignition OFF, disconnect the harness connector at the trailer box converter module.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 3 and ground.

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

3. Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

• | Backup lamp terminal 12

• | Park lamp terminal 4

• | Stop lamp terminal 5

• | Turn signal lamp - left terminal 9

• | Turn signal lamp - right terminal 10

4. Ignition ON, command the appropriate Light Test listed below On and Off with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• | Reverse Light Test

• | Parking Light Test

• | Brake Light Test

• | Rear Turn Signal Test

⇒ | If the test lamp is always ON, test the signal circuit for a short to voltage.

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

5. Ignition OFF, connect the harness connector at the trailer box converter module.
6. Connect a test lamp between the appropriate control circuit terminal listed below at the trailer connector and ground.

• | Backup lamp terminal 2

• | Park lamp terminal 7

• | Stop lamp terminal 6

• | Turn signal lamp - left terminal 1

• | Turn signal lamp - right terminal 4

7. Ignition ON, command the appropriate Light Test listed below On and Off with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• | Reverse Light Test

• | Parking Light Test

• | Brake Light Test

• | Rear Turn Signal Test

⇒ | 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, replace the trailer box converter module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.