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Stop Lamps Malfunction




Stop Lamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit/System Description

The BCM controls the stop lamps based on the input from the stop lamp switch. When the BCM detects the brake pedal is depressed, B+ is applied to the stop lamp relay control circuit energizing the Stop Lamp PCB Relay. With the relay energized, B+ is applied to the stop/turn lamp supply voltage circuits illuminating both stop lamps. At the same time the BCM applies B+ to the center high mounted stop lamp (CHMSL), transmission control module (TCM), and engine control module (ECM).

Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, observe the rear turn signals while commanding the left and right turn signals ON and OFF with a scan tool. The left and right rear turn signals should illuminate and flash when commanded ON.

• If the rear turn signals do not operate as specified, refer to Turn Signal Lamps and/or Indicators Malfunction (Turn Signal Lamps and/or Indicators Malfunction).

2. Ignition ON, observe the scan tool Stop Lamp Switch Status parameter while the brake pedal is applied. The reading should change from 1023 Counts to 1 Count as the brake pedal is applied.

• If the Stop Lamp Switch Status reading does not change between the specified values, refer to the Stop Lamp Switch Malfunction.

3. Observe the stop lamps as the brake pedal is applied and released. The stop lamps should turn ON and OFF as the brake pedal is applied and released.

• If one or more stop lamps do not illuminate, refer to Stop Lamp Malfunction
• If the stop lamps illuminate, but the CHMSL does not illuminate, refer to the Center High Mounted Stop Lamp Malfunction.

4. Ignition ON, with a test lamp connected to ground, probe each of the test points on the AUX STOP LAMP fuse while pressing and releasing the brake pedal. The test lamp should turn ON and OFF at one or both of the fuse test points.

• If the test lamp does not turn ON or remains ON at either test point, refer to the Auxiliary Stop Lamps PCB Relay Test.
• If the test lamp turns ON and OFF as the brake pedal is pressed and released, but the auxiliary stop lamps are inoperative, refer to the Auxiliary Stop Lamp Malfunction.

Circuit/System Testing

Stop Lamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Verify that a test lamp illuminates between the 12-volt reference circuit terminal C and ground.

• If the test lamp does not illuminate, test the 12-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, verify the scan tool Stop Lamp Switch Status parameter reading is 1 Count.

• If greater than the specified value, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the BCM.

4. Connect a 3A fused jumper wire between the signal circuit terminal D and the voltage reference circuit terminal C. Verify the scan tool Stop Lamp Switch Status parameter is 1023 Counts.

• If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

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

Center High Mounted Stop Lamp Malfunction
1. Ignition OFF, disconnect the harness connector at the CHMSL.
2. Ignition OFF, test for less than 5.0 ohms between the ground circuit terminal B and ground.

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

3. Connect a test lamp between the control circuit terminal A and the ground.
4. Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF as the brake pedal is applied and released.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
• 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 BCM.

5. If all circuits test normal, replace the CHMSL.

Auxiliary Stop Lamps PCB Relay Test
1. Ignition OFF, disconnect the X5 harness connector at the BCM.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 5 and B+.

• If the test lamp illuminates, test the control circuit for a short to voltage.

3. Ignition ON, connect a 3A fused jumper wire between the control circuit terminal 5 and B+. Verify that the stop lamps illuminate.

• If the stop lamps do not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

4. If all circuits test normal, replace the BCM.

Auxiliary Stop Lamp Malfunction
1. Ignition OFF, disconnect the X405 inline harness connector.
2. Test for less than 5 ohms between the ground circuit terminal G and ground.

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

3. Connect a test lamp between the control circuit terminal C and ground.
4. Ignition ON, verify that the test lamp turns ON and OFF while pressing and releasing the brake pedal.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
• 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 underhood fuse block.

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

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Stop Lamp Switch Replacement (Service and Repair)
* Tail Lamp Replacement (Tail Lamp Replacement)
* High Mount Stop Lamp Replacement (Service and Repair)
* Accessory Wiring Junction Block Replacement (Accessory Wiring Junction Block Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming

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