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 body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the stop lamp switch. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL).
Reference Information
Schematic Reference
Exterior Lights Schematics (Exterior Lights Diagrams)
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, command the stop lamps ON and OFF with a scan tool. The stop lamps should turn ON and OFF as commanded.
• If all stop lamps are inoperative, Refer to Stop Lamps Inoperative - All.
• If one or more, but not all, stop lamps are inoperative, Refer to Stop Lamps Inoperative - One or More.
• If the stop lamps are always illuminated, Refer to Stop Lamps Always ON.
2. Command the stop lamps ON and OFF using the stop lamp switch. Verify the scan tool Stop Lamp Switch Status parameter cycles between Active and Inactive as commanded.
• If the parameter does not cycle between the specified values, Refer to Stop Lamp Switch Malfunction.
Circuit/System Testing
Stop Lamps Inoperative - All
1. Ignition OFF, disconnect the STOP LAMP relay.
2. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
3. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
4. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
5. Command the stop lamps 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 ground. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
6. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
7. Disconnect the harness connector at the left tail lamp.
8. Test for less than 5.0 ohms between the ground circuit terminal C and ground.
• If greater than the specified range, test the ground circuit for a open/high resistance.
9. Verify that a test lamp illuminates between the control circuit terminal F and ground.
• If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.
10. If all circuits test normal, test or replace the STOP LAMP relay.
Stop Lamps Inoperative - One or More
1. Ignition OFF, disconnect the harness connector at the appropriate stop lamp.
2. Test for less than 5.0 ohms between the ground circuit listed below and ground:
* CHMSL - Terminal 2
* Stop lamp - Terminal C
• If greater than the specified range, test the ground circuit for a open/high resistance.
3. Verify that a test lamp illuminates between the control circuit listed below and ground:
* CHMSL - Terminal 1
* Stop lamp - Terminal F
• If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.
4. If all circuits test normal, test or replace the appropriate bulb or lamp assembly.
Stop Lamps Always ON
1. Ignition OFF, disconnect the STOP LAMP relay.
2. Ignition ON, verify that the stop lamps are not illuminated.
• If the stop lamps are illuminated, test the control circuit for a short to voltage.
3. Ignition ON, verify a test lamp does not illuminate between B+ and the control circuit terminal 86.
• If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
4. If all circuits test normal, replace the STOP LAMP relay.
Stop Lamps Inoperative From Stop Lamp Switch
1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Verify the scan tool Stop Lamp Switch Status parameter is Inactive.
• If not the specified value, test the signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the BCM.
3. Verify that a test lamp illuminates between the reference voltage circuit terminal 1 and ground.
• If the test lamp does not illuminate, test the reference voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
4. Install a 3A fused jumper wire between the signal circuit terminal 2 and the reference voltage circuit terminal 1. Verify the scan tool Stop Lamp Switch Status parameter is Active.
• 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, replace the stop lamp switch.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Stop Lamp Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming