GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The stop lamp switch signal circuit is a direct hardwire input to the throttle actuator control (TAC) module from the body control module (BCM). The TAC module monitors the stop lamp switch signal circuit in order to detect when the brake pedal has been applied. When the brake pedal is pressed, the BCM sends a class 2 serial data message to the powertrain control module (PCM) indicating that the brake pedal has been applied. The BCM also sends a high voltage signal on the stop lamp switch signal circuit to the TAC module. The TAC module sends a universal asynchronous receiver transmitter (UART) serial data message to the PCM indicating that a brake pedal application has occurred. The PCM will compare the UART serial data message and the class 2 serial data message in order to confirm that both serial data messages match.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1574 Stoplamp Switch Circuit

Conditions for Running the DTC

    •  DTC P0573 is not set.
    • The engine speed is greater than 700 RPM.
    • The traction control system (TCS) or the antilock brake system (ABS) are not active and have not failed.
    • The vehicle speed is greater than 48 km/h (30 mph) in order to enable the diagnostic.
         The diagnostic will disable when the wheel speed is less than 16 km/h (10 mph).

Conditions for Setting the DTC

    • The PCM detects that there is a 4.2 km/h (2.6 mph) or greater decrease in vehicle speed within 0.25 second.
    • The TAC module does not detect a voltage signal on the stop lamp switch signal circuit.

Action Taken When the DTC Sets

    • The Cruise Control System is disabled.
    • The PCM stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

Conditions for Clearing the DTC

    • A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if failures are not reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the DTC.

Diagnostic Aids

In order to avoid a misdiagnosis, inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.

For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Step

Action

Yes

No

Schematic Reference: Cruise Control Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views in Engine Controls - 3.5L (LX9)

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Is DTC P0573 current in the powertrain control module (PCM)?

Go to DTC P0573 in Lighting Systems

Go to Step 3

3

Do the stop lamps operate properly?

Go to Step 4

Go to Stop Lamps Inoperative in Lighting Systems

4

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the Stoplamp Status parameter in the Body and Accessories Cruise Control data list.

Does the Stoplamp Status parameter display On?

Go to Step 5

Go to Diagnostic Aids

5

Test the stop lamp switch signal circuit for an open or for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 6

6

Inspect for poor connections at the harness connector of the throttle actuator control (TAC) module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 7

7

Replace the TAC module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 8

--

8

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

Does the DTC reset?

Go to Step 2

System OK