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P codepowertrainMedium severity

P0571Cruise Control/Brake Switch "A" Circuit

A fault has been detected in the brake switch circuit that tells the cruise control system when the brake pedal is pressed.

Definition

The PCM monitors the brake pedal switch (circuit "A") both to disengage cruise control instantly and, on many vehicles, to cross-check the brake light circuit. P0571 sets when the switch signal is implausible — for example brake-on indicated while the vehicle accelerates, or the two brake switch contacts disagree. Symptoms include cruise control that will not set or drops out, brake lights stuck on or off, and on some transmissions a torque converter clutch that will not apply or release correctly. Because the same switch often controls the brake lights and shift interlock, this fault has a real safety dimension even though it rarely lights the MIL.

Common causes

  • Failed or misadjusted brake light (stop lamp) switch at the pedal
  • Blown brake light fuse removing power from the switch circuit
  • Corroded or damaged wiring/connector at the brake switch
  • Worn brake pedal bushings or a missing pedal stop pad changing switch actuation
  • Aftermarket trailer wiring or brake controller backfeeding the circuit
  • Faulty PCM input (rare)

Common misdiagnoses

  • Replacing the cruise control switch on the steering wheel
  • Replacing the ABS module for what is a simple pedal switch fault
  • Replacing the vehicle speed sensor
  • Replacing the PCM before checking the brake light fuse and switch adjustment

Troubleshooting steps

  1. 1.Verify brake light operation first

    Have a helper press the pedal and confirm all brake lamps work; no brake lights points to the fuse, switch, or its power feed.

  2. 2.Watch the brake switch PIDs on a scan tool

    Most vehicles show two brake switch states; both should change simultaneously with a light pedal press and never disagree.

  3. 3.Test the switch with a multimeter

    Check for correct open/closed continuity at the specified pedal travel and verify battery voltage on the feed circuit with the key on.

  4. 4.Check switch adjustment at the pedal

    Confirm the switch plunger fully extends at rest and actuates within the first inch of pedal travel; adjust or shim per the service manual.

  5. 5.Inspect wiring for backfeeds and shorts

    Look closely at trailer harness splices and connector corrosion that can hold the circuit high or low.

  6. 6.Clear the code and road test

    Confirm cruise sets, disengages immediately with the pedal, and the code does not return.

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