Powertrain (Engine & Gearbox)Standard EOBD

P0571 - Brake Switch "A" Circuit

Q: What are the symptoms of fault code P0571?

• Cruise Control is inoperative • Brake lights stay on continuously or fail to illuminate • ABS/ESC warning lights may be triggered • Shift interlock failure (cannot shift out of 'Park' on automatics) • Check Engine Light (MIL) illuminated

Q: What causes fault code P0571?

• Most likely: Faulty brake light switch (internal mechanical or electrical failure) • Likely: Incorrectly adjusted brake switch at the pedal assembly • Possible: Damaged wiring harness or corroded connectors between the switch and ECM • Rare: Installation of non-compatible LED brake light bulbs (causing circuit resistance issues) • Very rare: Software glitch or internal fault in the Engine Control Module (ECM/BCM)

Q: How do you fix fault code P0571?

STEP 1: Verify brake light operation. If all lights are out, check fuses first. STEP 2: Perform a visual inspection of the brake switch located at the pedal assembly. Look for loose wiring or mechanical damage. STEP 3: Electrical testing. Measure input voltage (should be 12V). Use an ohmmeter to check continuity; resistance should be ~0 Ohms when pressed and infinite when released. STEP 4: Use a scan tool to monitor 'Brake Switch State' in the live data stream. If the state remains static while pumping the pedal, the switch is defective. STEP 5: Clear DTCs and perform a test drive to confirm the cruise control engages.

Last updated:1 February 2026

Related:Connector, Brake Light Switch, Engine Control Module (ECM), Brake Control Module (BCM), Fuse

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0500

Vehicle Speed Sensor (VSS) 'A' Range/Performance

P0501

Vehicle Speed Sensor 'A' Range/Performance

P0502

Vehicle Speed Sensor 'A' Circuit Low Input

P0503

Vehicle Speed Sensor (VSS) Intermittent/Erratic/High

Technical Description

P0571 is a generic OBD-II diagnostic trouble code (DTC) indicating a malfunction within the brake switch 'A' circuit. The brake switch provides a critical input to the Engine Control Module (ECM) and Body Control Module (BCM) to signal when the brake pedal is depressed. This signal is used to disengage the Cruise Control system and to manage engine torque requests during braking. The fault is triggered if the ECM detects an implausible signal, an open circuit, or a short to voltage/ground. Modern vehicles use redundant signals; a mismatch between the primary brake switch and the secondary/CAN-based signals will store this code.

Possible Causes

Faulty brake light switch (internal mechanical or electrical failure)

Incorrectly adjusted brake switch at the pedal assembly

Damaged wiring harness or corroded connectors between the switch and ECM

Installation of non-compatible LED brake light bulbs (causing circuit resistance issues)

Very rare: Software glitch or internal fault in the Engine Control Module (ECM/BCM)

Symptoms

Cruise Control is inoperative

Brake lights stay on continuously or fail to illuminate

ABS/ESC warning lights may be triggered

Shift interlock failure (cannot shift out of 'Park' on automatics)

Check Engine Light (MIL) illuminated

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P0571 - Brake Switch "A" Circuit

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P0571 - Brake Switch "A" Circuit

Related Fault Codes

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Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have other fault codes?

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