GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 C-Series Medium Duty Truck C6/7/8 - Mexico 🢒 DTC 🢒 DTC P1574

Circuit Description

This diagnostic test functions on the assumption that a sudden decrease in vehicle speed is caused by a brake pedal application. When the powertrain control module (PCM) detects that there is a 4.2 km/h (2.6 mph) or greater decrease in vehicle speed within 0.25 seconds and a transition of the torque converter clutch (TCC) brake switch without a transition of the stop lamp switch, the PCM sets DTC P1574.

Conditions for Running the DTC
    • The engine speed is greater than 700 RPM.
    • The traction control system or the antilock brake system 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 vehicle speed decreases by at least 4.2 km/h (2.6 mph) within 0.25 seconds.
    • The PCM detects a TCC brake switch/cruise control release signal transition.
    • The PCM does not detect a stop lamp switch transition.

Action Taken When the DTC Sets
    • The PCM sets the stop lamp switch status to released.
    • The PCM disables the operation of the cruise control system.

Conditions for Clearing the DTC
    •  A history DTC will clear after 40 malfunction free warm-up cycles.
    • The PCM receives a clear code command from the scan tool.

Diagnostic Aids

Refer to Exterior Lighting Systems Description and Operation in Lighting Systems in order to avoid a misdiagnosis.

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

1

Did you perform the Cruise Control Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Cruise Control

2
  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Depress the brake pedal.
  4. With the scan tool, observe the Stop lamp Pedal Switch parameter in the PCM Cruise Control data list.

Does the Stop lamp Pedal Switch parameter display Released?

Go to Step 3

Go to Diagnostic Aids

3

Do the stop lamps operate properly?

Go to Step 4

Go to Stop Lamps Inoperative in Lighting Systems

4

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

Did you complete the repair?

Go to Step 5

--

5
  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