Stop Lamps Malfunction
Stop Lamps Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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/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).
Circuit/System Verification
1. Ignition ON, observe the scan tool Brake Applied Output Signal parameter as you apply and release the brake pedal. The reading should cycle between OFF and ON as the brake pedal is applied and released.
• If the reading does not change as the brake pedal is applied and released, refer to the Stop Lamp Switch Test.
2. 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 the stop lamps do not turn ON or always remain ON, refer to the Stop Lamp Circuit Test.
3. If the stop lamps function normal, but the center high mounted stop lamp (CHMSL) does not turn ON, refer to the Center High Mounted Stop Lamp Test.
Circuit/System Testing
Stop Lamp Switch Test
1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Verify that a test lamp illuminates between the B+ circuit terminal B and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
3. Connect a 3A fused jumper wire between the signal circuit terminal A and B+. Verify the scan tool Brake Applied parameter is On.
• 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.
4. If all circuits test normal, test or replace the stop lamp switch.
Stop Lamps Circuit Test
1. Ignition ON, with a test lamp connected to ground, probe each of the test points on the Stop Lamp fuse while pressing and releasing the brake pedal. The test lamp should illuminate at one or both of the fuse test points.
• If the test lamp does not illuminate or remains illuminated at either test point, refer to the Stop Lamps PCB Relay Test.
2. Ignition OFF, disconnect harness connector at the inoperative stop/turn lamp assembly.
3. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal G and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
4. Connect a test lamp between the supply voltage circuit terminal A and ground.
5. Ignition ON, command the appropriate LR or RR Turn Signal 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
6. If all circuits test normal, replace the inoperative stop/turn signal lamp assembly.
Stop Lamps PCB Relay Test
1. Ignition OFF, disconnect the X3 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal 30 and ground.
3. Ignition ON, press and release the brake pedal. 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 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.
4. If all circuits test normal, replace the underhood fuse block.
High Mounted Stop Lamp Circuit Test
1. Ignition OFF, disconnect the harness connector at the CHMSL.
2. Ignition OFF, test for less than 5.0 ohms of resistance 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 supply voltage 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the BCM.
• If the test lamp is always OFF, test the supply voltage 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.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Stop Lamp Switch Replacement
* Tail Lamp Replacement
* High Mount Stop Lamp Replacement