P0571
Brake Switch A Circuit
If your vehicle's onboard computer has flagged the diagnostic trouble code P0571, it refers to a detected anomaly regarding "Brake Switch A Circuit". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
The diagnostic trouble code P0571 indicates an active fault in the brake switch a circuit circuit or component. Drivers typically experience cruise control won't engage, brake lights stay on or won't turn on, shift interlock stuck when this code is active. This is a moderate-severity fault — plan a repair shop visit within the week to keep it from escalating.
Symptoms
Cruise control won't engage, brake lights stay on or won't turn on, shift interlock stuck
Common Causes
- Misadjusted brake light switch
- Failed brake light switch
- Blown brake light fuse
- Damaged wiring to switch
How to Fix
- 1 Adjust brake switch depth
- 2 Replace brake pedal switch
- 3 Check and replace related fuses
- 4 Repair wiring harness
Technical Explanation
Detection of P0571 occurs when the ECM cross-references multiple sensor inputs and determines that the reported values are physically inconsistent or out-of-range. A two-trip detection strategy is employed for most powertrain codes: the fault must be detected on one drive cycle, the vehicle key-cycled off, and the fault detected again on the next drive cycle before the MIL illuminates and a permanent DTC is stored. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
Code P0571 allows for cautious short-distance driving, but the underlying cause — most likely misadjusted brake light switch — will worsen with time. Fuel economy suffers, and ignoring the fault for weeks can turn a $10 fix into a much larger repair bill.
Mechanic's Pro Tip
Before replacing any component on P0571, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
Fuse: $10; Brake switch: $50 - $150