GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC W-Series Commercial W4 (W3500/W4500) 🢒 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/cruise release signal without a transition of the stop lamp switch, the PCM sets DTC P1574.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1574 Stop Lamp Switch Circuit

Conditions for Running the DTC
    •  DTCs P0502, P0503, P0719, and P0724 are not set.
    • The engine speed is greater than 700 RPM.
    • The traction control system (TCS) 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).
    • DTC P1574 runs continuously when the above conditions are met.

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/cruise 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

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

Step

Action

Yes

No

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. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Depress the brake pedal.
  4. With the scan tool, observe the Stoplamp Pedal Switch parameter in the powertrain control module (PCM) Cruise Control Data list.

Does the Stoplamp 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

4

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