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.

### DTC Descriptor

DTC P0812 : Reverse Position Switch Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Reverse Switch Signal | P0812 | 1 | 1 | --
Ground | -- | 1 | 1 | --
1. Backup Lamps Malfunction

### Circuit/System Description

The reverse gear switch is a normally open switch that closes with the reverse gear engagement. When the switch is open the engine control module (ECM) should detect a high signal voltage input. When the switch is closed the ECM should detect a low signal voltage input.

### Conditions for Running the DTC

• | No VSS faults exist.

• | Reverse switch is ON.

### Conditions for Setting the DTC

The ECM detects circuit failure of the reverse input switch.

### Action Taken When the DTC Sets

DTC P0812 is type C DTC.

### Conditions for Clearing the DTC

DTC P0812 is type C DTC.

### 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

Ignition ON, observe the scan tool Reverse Switch parameter. The reading should be Off and change to On when the transmission is shifted into reverse.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the reverse switch.
2. Ignition OFF, test for less than 1 ohm between the ground circuit terminal 1 and ground.

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

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

⇒ | If not the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the ECM.

4. Ignition ON, install a 3-amp fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Reverse Switch parameter is On.

⇒ | 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 ECM.

5. If all circuits test normal, test or replace the reverse switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for the ECM replacement, setup, and programming