GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The body control module (BCM) supplies battery positive voltage to the center high mounted stop lamp (CHMSL) through the stop lamp supply voltage circuit when the brakes are applied. The stop lamp supply voltage circuit also supplies a signal to the powertrain control module (PCM) and the electronic brake control module (EBCM) for other functions, is a separate pin in the BCM connector, and is internally connected within the BCM.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3445 Stop Lamp Circuit

Conditions for Running the DTC

    • The battery voltage must be between 9-16 volts.
    • The brake pedal must be applied.

Conditions for Setting the DTC

    • When the BCM detects a short to ground in the stop lamp supply voltage circuit to the CHSML.
    • When the BCM never detects an open, indicating a BCM fault.
    • When the BCM detects a short to ground in the stop lamp supply voltage circuit to another module.

Action Taken When the DTC Sets

The CHMSL will not operate.

Conditions for Clearing the MIL/DTC

    • This DTC will clear on current status after the condition for setting the fault is corrected.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • History and current DTCs can be cleared using a scan tool.

Diagnostic Aids

    • Perform a visual inspection for loose or poor connections at all related components. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • A short to ground in either stop lamp supply voltage circuits (CHSML or other module) may cause this DTC.

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Turn ON the ignition, with the engine OFF.
  2. Apply the brake pedal.

Does the center high mounted stop lamp (CHMSL) illuminate?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Test for a short to ground in the stop lamp supply voltage circuit of the CHMSL. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 4

4

Test for a short to ground in the stop lamp supply voltage circuit of the other modules connected to this circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 5

5

Replace the body control module (BCM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 6

--

6

  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK