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
Diagnostic Fault Information
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) 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 and the PCM. The TAC module sends a serial data message to the PCM indicating that a brake pedal application has occurred. The 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 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 PCM sets DTC P1574.
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 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.
Action Taken When the DTC Sets
* The cruise control system is disabled.
* The PCM stores the DTC information into memory when the diagnostic runs and fails.
* The malfunction indicator lamp (MIL) will not illuminate.
* The PCM records the operating conditions at the time the diagnostic fails. The 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.
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
Important: 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).
Repair any brake system related DTCs before performing this diagnostic.
Ignition ON, observe the Stop Lamp Pedal Switch parameter in the 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
1. Ignition OFF, disconnect the X1 harness connector at the PCM and the TAC module.
2. Connect a test lamp between the TAC module harness connector terminal 6 and ground.
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 stoplamp switch 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.
5. Connect a test lamp between the PCM connector X1 terminal 32 and ground.
6. Ignition ON, press and release the brake pedal. Verify he test lamp turns ON and OFF when pressing and releasing the brake pedal.
• If the test lamp is always OFF, test the stoplamp switch signal circuit for an open/high resistance. If the circuit tests normal, replace the TAC module.
7. If all circuit tests normal, replace the TAC module. Clear the DTC and road test the vehicle. If DTC P1574 resets as current, replace the 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 PCM or TAC module replacement, setup, and programming