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
--- | --- | --- | --- | ---
Brake Lamp Switch Voltage Supply Circuit | 2 | 2 | -- | --
Brake Lamp Switch Signal Circuit | 2 | 2 | 1 | --
Brake Lamp Bulb Ground Circuit | -- | 2 | -- | --
Stop Lamp Switch | 2 | 2 | 1 | --
1. Brake Lamps Always ON 2. Brake Lamps Inoperative

### Circuit/System Description

The stop lamp switch is supplied voltage by the brake fuse. When the brake pedal is pressed the stop lamp switch closes supplying voltage to the stop lamp light bulbs.

### Diagnostic Aids

A short to ground, a short to voltage in the following location may cause a malfunction to occur:

• | The brake switch ground circuit

• | The brake switch

### Reference Information

#### Schematic Reference

Exterior Lights Schematics

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data Definitions

• | Scan Tool Data List

• | Scan Tool Output Controls

### Circuit/System Verification

Engage the brake pedal, observe the brake lights. The brake lights should turn ON when the brake pedal is depressed.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Verify that the stop lamps are OFF.

⇒ | If the stop lamps are not OFF, test the stop lamp signal circuits for a short to voltage.

3. Verify that a test lamp illuminates between the voltage supply circuit and ground.

⇒ | If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance. If the voltage supply circuit fuse is open, test or replace the stop lamp switch.

4. Install a 3-amp fused jumper wire between the signal circuit and the voltage supply circuit. Verify that the brake lamps are ON.

⇒ | If the brake lamps are not ON, test the signal circuit for an open/high resistance. If circuit tests normal, test or replace the brake lamp bulb.

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

### Component Testing

#### Stop Lamp Switch Testing

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Test for infinite resistance between the signal terminal and the voltage supply terminal with the switch in the open position.

⇒ | If less than infinite resistance, replace the stop lamp switch.

3. Test for less than 1 ohm of resistance between the signal terminal and the voltage supply terminal with the switch in the closed position.

⇒ | If greater than 1 ohm, replace the stop lamp switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Stop Lamp Switch Replacement

• | Stop Lamp Switch Adjustment