P1574

DTC P1574

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P1574
- Stop Lamp Switch Circuit

Diagnostic Fault Information





Circuit/System Description

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 malfunction indicator lamp (MIL) will not illuminate.
* The cruise control system is disabled.

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 (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Cruise Control Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

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

* PCM X1 and TAC module (L26)
* ECM X1 and TCM (LD8)

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

* TAC terminal 6 (L26)
* TCM terminal 42 (LD8)

3. Ignition ON, press and release the brake pedal. Verify the test lamp turns ON and OFF when 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.

4. Ignition OFF, connect the harness connector at the TAC module (L26) or the TCM (LD8).
5. Connect a test lamp between the appropriate signal circuit terminal listed below and ground.

* PCM terminal 32 X1 (L26)
* ECM terminal 7 X1 (LD8)

6. Ignition ON, press and release the brake pedal. Verify the test lamp turns ON and OFF when pressing and releasing the brake pedal.

• If the test lamp is always OFF, test the signal circuit for an open/high resistance. If the circuit test normal, replace the TAC module (L26) or the TCM (LD8).

7. If all circuit tests normal, replace the PCM (L26) or the ECM (LD8).

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Control Module References (Programming and Relearning) for BCM, PCM, or TAC module replacement, setup, and programming