P1574
DTC P1574
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.
DTC Descriptor
DTC P1574 00
- Stop Lamp Switch Circuit
Circuit/System Description
The stop lamp switch signal circuit is a direct 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 serial data message to the powertrain control module (PCM)/engine control module (ECM) 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 serial data message to the PCM indicating that a brake pedal application has occurred. The ECM/PCM compares the serial data messages from the BCM and TAC modules in order to confirm that both serial data messages match.
This diagnostic test functions on the assumption that a sudden decrease in vehicle speed is caused by a brake pedal application. When the ECM/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/cruise release switch without a transition of the stop lamp switch, the ECM/PCM sets DTC P1574.
Diagnostic Fault Information
Conditions for Running the DTC
* DTC P0573 is not set.
* 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.
Conditions for Setting the DTC
* The vehicle speed decreases by at least 4.2 km/h (2.6 mph) within 0.25 seconds.
* The TAC module does not detect a voltage signal on the stop lamp switch signal circuit.
* The ECM/PCM does not detect a stop lamp switch transition.
Action Taken When the DTC Sets
* The cruise control system is disabled.
* The ECM/PCM stores the DTC information into memory when the diagnostic runs and fails.
* The malfunction indicator lamp (MIL) will not illuminate.
* The ECM/PCM records the operating conditions at the time the diagnostic fails. The ECM/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 without a repeated failure.
Diagnostic Aids
Important: Repair any brake system related DTCs before performing this diagnostic.
In order to avoid a misdiagnosis, perform the following:
* If a BCM has been replaced, the brake pedal position (BPP) sensor must be calibrated. Refer to Brake Pedal Position Sensor Calibration (Programming and Relearning) .
* Inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation) .
Reference Information
Schematic Reference
* Cruise Control Schematics (Electrical Diagrams)
* Exterior Lights Schematics (Exterior Lights Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
* Cruise Control Description and Operation (Description and Operation)
* Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Circuit/System Verification
Ignition ON, observe the Stop Lamp Pedal Switch parameter in the ECM/PCM while applying and releasing the brake pedal. The reading should change between Applied/Released, and all brake lights should turn on and off accordingly.
Circuit/System Testing
Important: Repair any Brake System related DTCs or symptoms before using this diagnostic.
1. Ignition ON, perform the brake pedal position (BPP) sensor calibration procedure and verify the BPP is calibrated properly. Refer to Brake Pedal Position Sensor Calibration (Programming and Relearning) .
• If the BPP will not calibrate properly, replace the BPP.
2. Ignition ON, apply the brake pedal and verify that the Stoplamp Pedal Switch parameter displays On or Applied.
• If the parameter reads Off or Released, test the stop lamp switch signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM/PCM.
3. If all circuits test normal, replace the ECM/PCM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Brake Pedal Position Sensor Replacement (Brake Pedal Position Sensor Replacement)
* Control Module References (Programming and Relearning)for ECM or PCM module replacement, setup, and programming