A common issue encountered by Seat Leon MK1 owners is the dreaded “Brake Switch (F): Implausible Signal” fault code (P0571) in VCDS. This article delves into diagnosing and resolving this problem, drawing from a real-world experience shared by a fellow MK1 owner.
Understanding the P0571 Fault Code in a Seat Leon MK1
The P0571 fault code indicates an inconsistency in the signal received from the brake light switch by the Engine Control Unit (ECU). This can lead to various issues, including a flashing glow plug light (a common symptom in the MK1 Leon) and potential problems with cruise control or other systems reliant on brake switch input. Although the car may run perfectly fine, addressing this fault is crucial.
Troubleshooting Steps Taken with VCDS-Lite
The owner, using VCDS-Lite, diagnosed the 16955/P0571 fault code and systematically attempted the following fixes:
- Brake Light Switch Replacement: The most common culprit for this error is a faulty brake light switch. Replacing it is usually the first step.
- Bulb Replacement: While brake lights might appear functional, faulty bulbs can sometimes contribute to this error. New bulbs were installed.
- Wiring Inspection and Repair: Faulty wiring, especially around areas where modifications like tow bar wiring have been made, can interfere with the brake switch signal. Bad scotch-locked connections were identified and repaired.
- Voltage Checks at ECU: Voltage readings were taken directly at the ECU connectors to ensure the signal from the switch was reaching the ECU correctly.
Despite these efforts, the fault code persisted, intermittently appearing and disappearing. The car itself exhibited no other drivability issues, and the engine management light was non-functional.
Further Diagnostic Possibilities for a Seat Leon MK1 with VCDS
With the common solutions exhausted, it’s time to explore less obvious causes:
- Ground Issues: A poor ground connection in the brake light circuit can cause erratic behavior. Inspecting and cleaning ground points related to the brake switch and ECU is recommended.
- Wiring Harness Damage: While obvious damage was already addressed, a thorough inspection of the entire brake light wiring harness for less visible damage, such as chafing or internal breaks, might reveal the problem.
- ECU Issues: Although less likely, a faulty ECU could be misinterpreting the brake switch signal. This requires more advanced diagnostics and potentially professional assistance.
- CAN Bus Communication Errors: Given the intermittent nature of the fault and the mention of a non-functional engine management light, there might be issues with communication on the CAN bus network. Further diagnostics using VCDS to check for communication errors in other modules might provide clues.
Conclusion and Next Steps
Troubleshooting the P0571 fault code in a Seat Leon MK1 can be challenging. While common solutions often resolve the issue, more in-depth diagnostics may be required for persistent problems. Further investigation into grounding, wiring harness integrity, and CAN bus communication is recommended. Tools like VCDS are invaluable for pinpointing the root cause and preventing unnecessary part replacements. Consulting with experienced Seat technicians or online forums dedicated to VCDS diagnostics can provide additional support.
