For 1990-2009 cars

## Backup Lamps Malfunction Automatic Transmission

### 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
--- | --- | --- | --- | ---
Backup Lamp Switch Signal | 1 | 1 | 1 | --
Backup Lamp - Left Control | B2545 00 | B2545 00 | 1 | --
Backup Lamp - Right Control | B3880 00 | B3880 00 | 1 | --
Left Rear Stop/Turn Lamp Ground | -- | 1 | -- | --
Park/Neutral Position Switch Ground | -- | 1 | -- | --
Right Rear Stop/Turn Lamp Ground | -- | 1 | -- | --
1. Backup Lamps Malfunction

### Circuit/System Description

The park/neutral position switch receives voltage from the underhood electrical center (UEC) via the backup lamp switch signal circuit. When the transmission is placed in the REVERSE position, the park/neutral position switch closes providing a ground path for the backup lamp switch signal circuit. The UEC responds to the flow of voltage by sending a serial data message to the rear electrical center (REC) requesting the backup lamps be illuminated. The REC applies battery voltage to the backup lamps control circuit illuminating the backup lamps. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the UEC via serial data requesting the REC to remove battery voltage from the backup lamps control circuit. The backup lamps are permanently grounded at G403.

### Reference Information

#### Schematic Reference

Exterior Lights 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, observe the scan tool Reverse Gear Switch parameter while operating the gear selector in and out of the reverse position. The parameter should change between Active and Inactive as the gear selector is operated.

⇒ | If the parameter does not change as the gear selector is operated, refer to Park/Neutral Position Switch Malfunction.

2. With a scan tool, command the Reverse Light Test ON and OFF. The backup lamps should turn ON and OFF when commanded.

⇒ | If the backup lamps do not illuminate when commanded, refer to Backup Lamps Malfunction.

### Circuit/System Testing

#### Park/Neutral Position Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the park/neutral position switch.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 9 and ground.

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

3. Ignition ON, verify the scan tool Reverse Gear Switch parameter is Inactive.

⇒ | If not the specified value, test the signal circuit terminal 7 for a short to ground. If the circuit tests normal, replace the UEC.

4. Install a 3A fused jumper wire between the signal circuit terminal 7 and ground. Verify the scan tool Reverse Gear Switch parameter is Active.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the UEC.

5. If all circuits test normal, replace the park/neutral position switch.

#### Backup Lamps Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative backup lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground.

• | Left tail lamp ground terminal 1 - 3 Door

• | Left tail lamp ground terminal 6 - 5 Door

• | Right tail lamp ground terminal 6 - 3 Door

• | Right tail lamp ground terminal 1 - 5 Door

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

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

• | Left backup lamp control terminal 2 - 3 Door

• | Left backup lamp control terminal 1 - 5 Door

• | Right backup lamp control terminal 5 - 3 Door

• | Right backup lamp control terminal 6 - 5 Door

4. Command the Reverse Light Test ON and OFF 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 circuit tests normal, replace the REC.

⇒ | 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 REC.

5. If all circuits test normal, replace the inoperative tail lamp circuit board.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Circuit Board Replacement

• | Park/Neutral Position Switch Installation

• | Control Module References for REC or UEC replacement, setup, and programming

## Backup Lamps Malfunction Manual Transmission

### 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
--- | --- | --- | --- | ---
Backup Lamp Switch Signal | 1 | 1 | 1 | --
Backup Lamp - Left Control | B2545 00 | B2545 00 | 1 | --
Backup Lamp - Right Control | B3880 00 | B3880 00 | 1 | --
Backup Lamp Switch Ground | -- | 1 | -- | --
Left Rear Stop/Turn Lamp Ground | -- | 1 | -- | --
Right Rear Stop/Turn Lamp Ground | -- | 1 | -- | --
1. Backup Lamps Malfunction

### Circuit/System Description

The underhood electrical center (UEC) provides the normally open backup lamp switch with voltage. When the transmission is placed in the reverse position, the backup lamp switch closes providing a ground path through G104. The UEC responds to the flow of voltage by sending a serial data message to the rear electrical center (REC) requesting the backup lamps be illuminated. The REC applies battery voltage to the backup lamps control circuit illuminating the backup lamps. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the UEC via serial data requesting the REC to remove battery voltage from the backup lamps control circuit. The backup lamps are permanently grounded at G403.

### Reference Information

#### Schematic Reference

Exterior Lights 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, observe the scan tool Reverse Gear Switch parameter while operating the gear selector in and out of the reverse position. The parameter should change between Active and Inactive as the gear selector is operated.

⇒ | If the parameter does not change as the gear selector is operated, refer to Backup Lamp Switch Malfunction.

2. With a scan tool, command the Reverse Light Test ON and OFF. The backup lamps should turn ON and OFF when commanded.

⇒ | If the backup lamps do not illuminate when commanded, refer to Backup Lamps Malfunction.

### Circuit/System Testing

#### Backup Lamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the backup lamp switch.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal A and ground.

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

3. Ignition ON, verify the scan tool Reverse Gear Switch parameter is Inactive.

⇒ | If not the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the UEC.

4. Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the scan tool Reverse Gear Switch parameter is Active.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the UEC.

5. If all circuits test normal, replace the backup lamp switch.

#### Backup Lamps Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative backup lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the appropriate ground circuit terminal listed below and ground.

• | Left tail lamp ground terminal 1 - 3 Door

• | Left tail lamp ground terminal 6 - 5 Door

• | Right tail lamp ground terminal 6 - 3 Door

• | Right tail lamp ground terminal 1 - 5 Door

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

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

• | Left backup lamp control terminal 2 - 3 Door

• | Left backup lamp control terminal 1 - 5 Door

• | Right backup lamp control terminal 5 - 3 Door

• | Right backup lamp control terminal 6 - 5 Door

4. Command the Reverse Light Test ON and OFF 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 circuit tests normal, replace the REC.

⇒ | 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 REC.

5. If all circuits test normal, replace the inoperative tail lamp circuit board.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Circuit Board Replacement

• | Backup Lamp Switch Replacement

• | Control Module References for REC or UEC replacement, setup, and programming