Faulty brake pedal position switch 'A' (worn contacts, sticking plunger, or internal failure).; Misadjusted or loose brake switch mounting bracket causing incorrect switch actuation.; Damaged, corroded, or disconnected wiring or connector at the brake switch or PCM.; Blown fuse or poor ground connection supplying power or ground to the brake switch circuit.; Failed brake light bulb or LED assembly causing abnormal current draw that affects switch signal plausibility.; PCM software issue or internal fault in the brake switch input circuit (rare but possible).; Aftermarket accessories wired into the brake circuit causing voltage irregularities.

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0571

P0571Brake Switch 'A' Circuit

Q: What does code P0571 mean?

Brake Switch 'A' Circuit. P0571 indicates that the powertrain control module (PCM) has detected an implausible signal or circuit fault on the brake pedal switch 'A' circuit, which is the primary input used to confirm brake pedal position. The computer compares this switch signal with other brake-related inputs and sets the code when the voltage or state does not match expected values during key-on or driving conditions.

P0571 indicates that the powertrain control module (PCM) has detected an implausible signal or circuit fault on the brake pedal switch 'A' circuit, which is the primary input used to confirm brake pedal position. The computer compares this switch signal with other brake-related inputs and sets the code when the voltage or state does not match expected values during key-on or driving conditions.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

The anti-lock brake system (ABS) warning light and traction control light may illuminate because the PCM cannot confirm brake pedal status.
Cruise control may fail to engage or may disengage unexpectedly when the brake pedal is pressed or released.
The transmission may hesitate to shift out of park or may exhibit harsh shifting due to incorrect brake pedal status.
Brake lights may stay on continuously or fail to illuminate when the pedal is pressed.
Often no symptoms besides the warning light, especially if the fault is intermittent or only affects the signal to the PCM.
Some vehicles may enter limp mode or limit engine power as a failsafe when brake switch plausibility is lost.

Common causes, most likely first

Faulty brake pedal position switch 'A' (worn contacts, sticking plunger, or internal failure).
Misadjusted or loose brake switch mounting bracket causing incorrect switch actuation.
Damaged, corroded, or disconnected wiring or connector at the brake switch or PCM.
Blown fuse or poor ground connection supplying power or ground to the brake switch circuit.
Failed brake light bulb or LED assembly causing abnormal current draw that affects switch signal plausibility.
PCM software issue or internal fault in the brake switch input circuit (rare but possible).
Aftermarket accessories wired into the brake circuit causing voltage irregularities.

How to diagnose and fix it

Verify the brake lights operate correctly with the pedal pressed and released; replace any faulty bulbs first.
Inspect the brake pedal switch 'A' for proper adjustment, secure mounting, and smooth plunger movement; adjust or replace as needed.
Check all fuses and grounds related to the brake switch circuit using a multimeter and wiring diagram.
Disconnect the brake switch connector and inspect terminals for corrosion, tightness, and correct voltage signals (power, ground, signal) with the key on.
Perform a continuity and voltage drop test on the signal wire between the brake switch and PCM to rule out high resistance or opens.
If the switch and wiring test good, substitute a known-good brake switch and clear the code to see if it returns.
As a last step, reprogram or replace the PCM only after confirming all external circuits are fault-free and the code persists.

Brake switch faults that mimic other failures

A sticking brake switch can cause the torque converter clutch to stay engaged or the transmission to shift erratically, leading to misdiagnosis of transmission problems.
The PCM often cross-checks the brake switch 'A' signal against the brake switch 'B' signal (if equipped) and the ABS wheel speed sensors; a mismatch can set P0571 even when the switch itself is functional.
Aftermarket LED brake light bulbs can draw too little current, causing the PCM to misinterpret the brake circuit state and set P0571 without any hard failure.
On some vehicles, a weak battery or poor ground can cause voltage spikes that momentarily confuse the brake switch input, setting an intermittent P0571 that never returns.
The brake switch 'A' circuit is also used by the cruise control and hill-start assist systems, so a fault may disable those features without obvious brake light symptoms.

Can I keep driving with P0571?

The vehicle is generally safe to drive if the brake lights work and the pedal feels normal, but avoid using cruise control and be aware that the transmission may shift abnormally. Have the fault diagnosed promptly because a failed brake switch can affect ABS and stability control operation.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.