Chevrolet Silverado / GMC Sierra. Service manual — part 2482

DTC B3884

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions 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

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

CHMSL Relay Control

B3884 00

1

2

-

CHMSL Control

1

1

2

-

CHMSL Relay Control

-

1

-

-

CHMSL Ground

-

1

-

-

1. Center High Mounted Stop Lamp (CHMSL) Inoperative

2. Center High Mounted Stop Lamp (CHMSL) Always On

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, press the brake pedal. The CHMSL should illuminate.

Circuit/System Testing

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

1. Ignition OFF, disconnect the harness connectors at the center high mounted stop lamp.

2. Test for less than 1.0 ohm of resistance between the ground circuit terminals 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 terminals A and ground circuit

terminals 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 Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Underhood Electrical Center or Junction Block Replacement

Control Module References for BCM replacement, setup, and programming

SYMPTOMS - LIGHTING

1. Perform the Diagnostic System Check - Vehicle , before using the Symptom Tables in

order to verify that all of the following are true:

There are no DTCs set.

The control modules can communicate via the serial data link.

2. Review the system operation in order to familiarize yourself with the system functions.

Refer to the following:

Exterior Lighting Systems Description and Operation

Interior Lighting Systems Description and Operation

Visual/Physical Inspection

Inspect for aftermarket devices which could affect the operation of the Lighting System.
Refer to Checking Aftermarket Accessories .

Inspect the easily accessible or visible system components for obvious damage or conditions
which could cause the symptom.

Intermittent

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to
Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the
symptom:

Backup Lamps Malfunction

Courtesy Lamps Malfunction (w/AN3) or Courtesy Lamps Malfunction (w/o AN3)

Daytime Running Lamps Malfunction

Exterior Courtesy Lamps Malfunction

Front Fog Lamps Malfunction

Hazard Lamps Malfunction

Headlamps Malfunction

Headlamps Flash to Pass Inoperative

High Beam Indicator Malfunction

Interior Backlighting Malfunction (w/AN3) or Interior Backlighting Malfunction
(w/o AN3)

Park, License, and/or Tail Lamps Malfunction

Reading Lamps Malfunction

Stop Lamps Malfunction

Turn Signal Lamps and/or Indicators Malfunction

Vanity Mirror Lamp Malfunction

BACKUP LAMPS MALFUNCTION

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado