P0571
Cruise Control/Brake Switch A Circuit MalfunctionP0571 is a generic OBD-II powertrain diagnostic trouble code: Cruise Control/Brake Switch A Circuit Malfunction. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0571 means
P0571 is set when the PCM/ECM detects an abnormal voltage or resistance condition in the brake switch 'A' circuit — the primary stop-light switch mounted on the brake pedal bracket. This switch serves several overlapping functions: it illuminates the brake lights, signals the PCM to disengage cruise control when the pedal is pressed, commands the torque converter clutch (TCC) to unlock on automatic transmissions, and on some platforms provides an idle-up signal or activates brake-specific emissions strategies. A single switch failure therefore cascades across multiple systems simultaneously.
The code often appears after brake light bulb replacement, brake pedal bushing replacement, or any repair that requires disconnecting or disturbing the pedal switch. The switch is highly adjustable on many vehicles and a misaligned or partially engaged switch can produce an intermittent or incorrect signal. On some vehicles the switch is dual-circuit (separate circuits for stop lights and PCM input), so one circuit can fail while the other appears normal, making diagnosis more nuanced.
Wiring faults — corroded connectors, chafed insulation, or a blown cruise control fuse — are common causes. A defective switch that fails to close or open correctly under pedal travel is the next most likely cause. PCM failure is rare but possible as a final diagnosis after all external circuit checks pass.
Common causes
Most-frequently reported root causes when P0571 is logged.
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1
Defective brake pedal switch (failed open, failed closed, or intermittent contact).
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2
Brake switch misadjusted on the pedal bracket after a pedal or bushing repair.
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3
Corroded, backed-out, or damaged connector at the brake switch.
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4
Chafed, open, or shorted wiring in the brake switch signal circuit to the PCM.
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5
Blown cruise control or brake switch fuse interrupting circuit power.
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6
Brake switch disturbed or disconnected during brake light bulb replacement.
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7
Failed PCM brake switch input circuit (rare, diagnose after ruling out all external causes).
Symptoms drivers notice
How to diagnose P0571
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scanner, record all stored codes and freeze frame data, and use live data to observe the brake switch status bit toggling as the pedal is pressed and released.
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2
Check the brake lights visually; non-functioning or continuously lit brake lights confirm a switch or circuit fault and help establish the direction of failure.
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3
Locate the brake switch on the pedal bracket and inspect for physical damage, corrosion at the connector, or obvious misalignment relative to the pedal arm.
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4
Check cruise control and brake switch fuses against the wiring diagram; replace any blown fuse and investigate the cause before re-energising the circuit.
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5
Use a digital multimeter to measure continuity and voltage across the switch terminals with the pedal at rest and fully depressed; compare readings to the service manual specification for both the stop-light circuit and the PCM signal circuit.
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6
If wiring and fuses are intact, adjust or replace the brake switch and verify correct pedal travel actuation before reassembling.
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7
Clear the code, road-test including a cruise control engagement and deactivation cycle, and confirm the code does not return.
Related powertrain codes
Frequently asked questions
Why did P0571 appear right after I changed a brake light bulb?
Brake light bulb replacement often requires reaching around the pedal assembly, which can inadvertently bump, rotate, or partially disconnect the brake switch. The switch is sensitive to its position on the bracket, so even slight disturbance can cause an out-of-tolerance signal.
Will P0571 prevent my cruise control from working?
Yes. The PCM uses the brake switch signal to cancel cruise control when the pedal is pressed. If the signal is absent or incorrect, most vehicles will disable cruise control engagement entirely as a safety measure.
Can P0571 affect my automatic transmission?
Yes on many vehicles. The PCM uses the brake switch signal to command torque converter clutch (TCC) unlock before a stop. A faulty signal can cause harsh TCC engagement, a shudder on deceleration, or prevent the clutch from unlocking correctly.
Is P0571 dangerous to drive with?
It depends on the failure mode. If the switch has failed open and brake lights are out, driving is unsafe and illegal. If the switch has failed closed with brake lights permanently on, following vehicles may not notice when you actually brake. Resolve the fault before driving.
Disabling P0571 in software
RaceTune can permanently disable P0571 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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