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Stop Lamps Malfunction




Stop Lamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (with HP2) (Initial Inspection and Diagnostic Overview)Diagnostic System Check - Vehicle (without HP2) (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

North American or European

The stop lamp switch is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a low reference signal and a B+ reference voltage to the stop lamp switch. When the stop lamp switch contacts close indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay control circuit and the center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the STOP LAMPS fuse to illuminate the left and right stop lamps.

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 scan tool Stop Lamp Relay Command parameter while pressing and releasing the brake pedal. The reading should change between ON and OFF.

• If not the specified value, refer to the Stop Lamp Switch Malfunction.

2. Ignition ON, observe the left, right and center high mount stop lamps while pressing and releasing the brake pedal. The stop lamps should turn ON and OFF.

• If the left and or right stop lamps are always ON or OFF, refer to the Stop Lamp Malfunction.

• If the center high mount stop lamp is always ON or OFF, refer to the Malfunction.

Circuit/System Testing

Stop Lamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, test for battery voltage between the 12-volt reference circuit terminal C and ground.

• If less than the specified range, 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. Verify the scan tool Stop Lamp Switch Status parameter is approximately 1023 counts.

• If not the specified value, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal D and the 12-volt reference circuit terminal C. Verify the scan tool Stop Lamp Switch Status parameter is 1 count.

• If not the specified value, test the signal circuit for 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.

Stop Lamp Malfunction
1. Ignition OFF, disconnect the harnes connector X4 at the BCM.
2. Ignition ON, verify a test lamp illuminates between the stop lamp B+ terminal 4 and ground.

• If the test lamp does not illuminate, and the STOP LAMPS fuse tests normal, test the B+ circuit for a short to ground or an open/high resistance.

3. Connect the harnes connector X4 at the BCM.
4. Ignition OFF, disconnect the harness connector at the appropriate stop lamp.
5. Test for less than 5.0 ohms between the listed ground circuit terminal below and ground.

* Tail/Stop and Turn Signal Lamp -Left and Right -Upper and Lower terminal GRD -with Z75 - E52
* Tail Lamp Circuit Board -Left and Right terminal D -with Z75 + E52 and European
* Tail/Stop Lamp -Left and Right terminal GRD -with X88
* Tail/Stop Lamp -Left and Right terminal G -Z88

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

6. Connect a test lamp between the listed stop lamp control circuit terminal and ground circuit terminal.

* Tail/Stop and Turn Signal Lamp -Left and Right -Upper and Lower terminal MJR -with Z75 - E52
* Tail Lamp Circuit Board -Left and Right terminal E -with Z75 + E52 and European
* Tail/Stop Lamp -Left and Right terminal MJR -with X88
* Tail/Stop Lamp -Left and Right terminal A -Z88

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

8. If all circuits test normal, test or replace the appropriate stop lamp.

CHMSL Malfunction
1. Ignition OFF, disconnect the harness connector X4 at the BCM.
2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 4 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground.

3. Reconnect the harness connector X4 at the BCM.
4. Ignition OFF, disconnect the harness connector at the center high mounted stop lamp (CHMSL).
5. 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.

6. Connect a test lamp between the stop lamp control circuit terminal A and ground circuit terminal B.
7. 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.

8. If all circuits test normal, test or replace the CHMSL.

Repair Instructions

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

* Stop Lamp Switch Replacement (Non-Adjustable Pedal) (Stop Lamp Switch Replacement (Non-Adjustable Pedal))Stop Lamp Switch Replacement (Adjustable Pedal) (Stop Lamp Switch Replacement (Adjustable Pedal))
* High Mount Stop Lamp Replacement (Yukon Two-mode Hybrid) (Service and Repair)High Mount Stop Lamp Replacement (Avalanche) (Service and Repair)High Mount Stop Lamp Replacement (Escalade) (Service and Repair)High Mount Stop Lamp Replacement (Yukon) (Service and Repair)
* Tail Lamp Bulb Replacement (Yukon) (Service and Repair)Tail Lamp Bulb Replacement (Cadillac) (Service and Repair)Tail Lamp Bulb Replacement (Tahoe, Avalanche) (Service and Repair)Tail Lamp Bulb Replacement (Tahoe) ()Tail Lamp Bulb Replacement (Yukon Two-mode Hybrid) ()
* Control Module References (Programming and Relearning) for BCM replacement, programming, and setup.

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