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
--- | --- | --- | --- | ---
Stop Lamp Switch B+ | 1 | 1 | -- | --
Stop Lamp Control | 1 | 1 | 1 | --
Stop Lamp Ground - Left | 1 | 1 | -- | --
Stop Lamp Ground - Right | -- | 1 | -- | --
Center High Mounted Stop Lamp (CHMSL) Ground - Left | -- | 1 | -- | --
Center High Mounted Stop Lamp (CHMSL) Ground - Right | -- | 1 | -- | --
1. Stop Lamps Malfunction

### Circuit/System Description

The STOP fuse in the underhood fuse block supplies battery voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery voltage is supplied to the electronic brake control module (EBCM), powertrain control module (PCM), left and right stop lamps, and the center high mounted stop lamp (CHMSL). The stop and CHMSL lamps are grounded at all times at G105.

### 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 Testing

#### Stop Lamp Circuit Test

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 1 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, and the B+ circuit fuse is open, test the signal circuit terminal 2 for a short to ground.

3. Connect the harness connector at the stop lamp switch.
4. Disconnect the harness connector at the inoperative stop lamp.
5. Test for less than 5 ohms between the listed ground circuit terminal and ground.

• | Left or Right stop lamp terminal G

• | Left or Right CHMSL terminal B

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

6. Connect a test lamp between the control circuit terminal A and ground. Press and release the brake pedel. The test lamp should turn ON and OFF.

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

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

7. If all circuits test normal, replace the inoperative stop lamp.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Bulb Replacement

• | Stop Lamp Switch Replacement

• | High Mount Stop Lamp Replacement