Diagnostic Instructions
DTC Descriptor
DTC P1574 00 : Stop Lamp Switch Circuit
Circuit/System Description
The stop lamp switch signal circuit is a direct hardwire 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 class 2 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 universal asynchronous receiver transmitter (UART) serial data message to the PCM indicating that a brake pedal application has occurred. The PCM (3.8L) / ECM (5.3L) will compare the UART
serial data message and the class 2 serial data message in order to confirm that both serial data messages match.
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 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, if failures are not reported by this or any other emission related diagnostic. |
Diagnostic Aids
Important: Repair any brake system related DTCs before performing this diagnostic.
In order to avoid a misdiagnosis, perform the following:
Reference Information
Schematic Reference
Cruise Control Schematics
Connector End View Reference
Lighting Systems Connector End Views
Description and Operation
Cruise Control Description and Operation
Electrical Information Reference
Scan Tool Reference
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: Fix any Brake System related DTCs or symptoms before using this diagnostic.
- 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
.
| ⇒ | If the BPP will not calibrate properly, replace the BPP. |
- 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 circuit tests normal, replace the ECM/PCM. |
- If all circuits test normal, replace the ECM/PCM.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
