B3884

DTC B3884

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.



DTC Descriptor
DTC B3884 00
- Center High Mounted Stop Lamp (CHMSL) Circuit




Diagnostic Fault Information






Circuit/System Description

When the brake pedal is applied, the brake pedal switch normally closed contact signal circuit voltage is interrupted to the body control module (BCM). Upon brake activation, the body control module (BCM) applies voltage through the CHMSL relay control circuit to the coil side of the relay. Ground is applied at all times to the other side of the CHMSL relay coil therefore the relay is now energized. Battery voltage is then applied through the switch side of the relay, the CHMSL fuse, and the CHMSL control circuit to the center high mounted stop lamp (CHMSL). The CHMSL is grounded at G 200.


Conditions for Running the DTC

* The ignition is ON.
* The stop lamps must be commanded ON.



Conditions for Setting the DTC

The BCM detects a short to ground in the CHMSL relay control circuit when the stop lamps are commanded ON.


Action Taken When the DTC Sets

The CHMSL does not illuminate.


Conditions for Clearing the DTC

* The conditions for setting the DTC are no longer present.
* A history DTC clears after 100 malfunction-free ignition cycles.



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 Testing

1. Ignition OFF, disconnect the harness connectors at the center high mounted stop lamp.
2. 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 stop lamp control circuit terminal A and ground circuit terminal B.
4. 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.

5. If all circuits test normal, test or replace the center high mounted stop lamp.



Repair Instructions

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

* Underhood Electrical Center or Junction Block Replacement (Underhood Electrical Center or Junction Block Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming