DTC P1574. Buick LaCrosse 2008

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2008 🢒 LaCrosse 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P1574

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
Stop Lamp Switch Signal	P1574	P1574	--	--

The stop lamp switch signal circuit is a direct hardwire input from the body control module (BCM) to the powertrain control module (PCM) and the throttle actuator control (TAC) module. The modules monitor the stop lamp switch signal circuit to detect when the brake pedal has been applied. When the brake pedal is applied, the BCM sends a serial data message to the modules and also a voltage signal on the stop lamp switch signal circuit indicating that the brake pedal has been applied.

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.

•	The vehicle speed is greater than 48 km/h (30 mph).

Conditions for Setting the DTC

•	The vehicle speed decreases by at least 4.2 km/h (2.6 mph) within 0.25 second.

•	The TAC module does not detect a voltage signal on the stop lamp switch signal circuit.

•	The PCM does not detect a stop lamp switch transition.

Actions Taken When the DTC Sets

•	The cruise control system is disabled.

•	The malfunction indicator lamp (MIL) will not illuminate.

Conditions for Clearing the DTC

•	The condition responsible for setting the DTC no longer exists.

•	A history DTC will clear after 40 malfunction-free ignition cycles have occurred.

Reference Information

Schematic Reference

•	Cruise Control Schematics

•	Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cruise Control 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 Testing

Ignition OFF, disconnect the harness connectors at the appropriate control modules listed below.

•	ECM X2 module and TCM (LY7)

•	ECM X1 module and TCM (LS4)

•	PCM X1 module and TAC (L26)

Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

•	TAC terminal 6 (L26)

•	TCM terminal 42 (LS4/LY7)

Ignition ON, verify the test lamp illuminates ON and OFF while pressing and releasing the brake pedal.

⇒	If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

Ignition OFF, connect the harness connector at the TCM or TAC.
Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

•	ECM terminal 59 (LY7)

•	ECM terminal 29 (LS4)

•	PCM terminal 32 (L26)

Ignition ON, verify the test lamp illuminates ON and OFF while pressing and releasing the brake pedal.

⇒	If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the appropriate TCM or TAC.

If all circuits tests normal, replace the appropriate ECM with (LS4/LY7), or PCM with (L26).

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM, ECM, PCM, TCM or TAC module replacement, setup, and programming