Fault code P0571 – a step-by-step guide to diagnosing and fixing it

Error code P0571 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system has detected a fault in the cruise control/speed control system brake signal circuit. This DTC P0571 indicates a problem with the brake light switch or its signal transmission to the engine control unit. For various manufacturers, this fault code may also be referred to as "Cruise Control/Speed Control Brake Switch 'A' Circuit Malfunction".

What causes can this error code have?

• Defective brake light switch
• Damaged wiring to the brake light switch
• Corroded or loose plug connections
• Incorrectly set brake light switch
• Defective engine control unit (ECU)
• Blown fuse in the brake light circuit
• Mechanical problems on the brake pedal
• Short circuit in the signal cable

What symptoms occur in parallel with fault code P0571?

• Cruise control malfunctions: The cruise control cannot be activated or switches off unexpectedly
• Brake light problems: The brake lights do not work or are permanently illuminated
• Shifting problems: Shifting problems may occur with automatic transmissions because the brake signal is required for gear selection
• Starting problems: The vehicle may not shift out of park
• Check engine light: The check engine light is permanently activated

How can the problem with error code P0571 be rectified?

• The repair requires a systematic diagnosis of the brake signal circuit and its components.
• Replace the brake light switch: Remove the defective switch on the brake pedal and replace it with a new original part, then adjust it correctly
• Repair wiring: Locate damaged cables to the brake light switch, repair severed areas or replace the entire cable set
• Clean plug connections: Disconnect all connectors in the brake light circuit, clean with contact spray and reconnect firmly
• Check and replace fuses: Locate the brake light circuit fuse in the fuse box and replace if necessary
• Adjust the brake light switch: Check the setting of the switch on the brake pedal and correct according to the manufacturer's specifications
• Replace engine control unit: If the ECU is defective, have the control unit replaced with a programmed spare part