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 transmission control module (TCM) from the body control module (BCM). The TCM module monitors the stop lamp signal circuit in order to detect when the brake pedal has been applied. When
the brake pedal is pressed, the BCM sends a High Speed GM Lan message to the engine control module (ECM) indicating that the brake pedal has been applied. The BCM also sends a high voltage signal on the stop lamp signal signal circuit to the TCM module. The
TCM module sends a universal asynchronous receiver transmitter low speed GM Lan message to the ECM indicating that a brake pedal application has occurred. The ECM will compare the GM LAN Low speed andGM LAN High Speed 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 Brake Pedal Position (BPP) signal circuit. |
| • | The ECM does not detect a Brake Pedal Position Sensor (BPP) transition. |
Action Taken When the DTC Sets
| • | The Cruise Control System is disabled. |
| • | The ECM stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The ECM records the operating conditions at the time the diagnostic fails. The ECM 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. |
| • | Use a scan tool in order to clear the DTC. |
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
Electrical Information Reference
Scan Tool Reference
Scan Tool Data List
Circuit/System Verification
Ignition ON, observe the Brake Pedal Position parameter in the ECM 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 sensor will not calibrate properly, replace the BPP sensor. |
- Ignition ON, apply the brake pedal and observe the BPP sensor parameter.
| ⇒ | If the parameter reads Applied, refer to
Stop Lamps Always On. If the stop lamps operate normal, replace the ECM. |
| ⇒ | If the parameter reads Released, test the BPP sensor signal circuit for an open/high resistance or short to ground. If circuit tests normal, replace the ECM. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
