P0571 Code: Cruise Control/Brake Switch A Circuit

What the P0571 code means

The brake pedal switch turns on the brake lights and tells the computer that the driver is braking. It is used to cancel cruise control, to release the shift lever on an automatic transmission and, on many vehicles, to start the engine.

It is a switch, so the computer sees a high or low voltage depending on its position. The P0571 code is stored when the circuit has an electrical fault, which can come from the switch, the wiring or the power supply.

If the signal is not correct, the brake lights can stay on or stay off, cruise control may not work and the shift lever may not come out of Park. The rubber stop on the pedal, which falls off over time, is a surprisingly common cause. Check the brake pedal switch (BPP sensor) itself to see how it is tested.

Always start with the simplest things: fuse, relay and connector. Then check power, ground and signal with the component connected (using back-probe pins), and finally the continuity of each wire to the computer. Replace the component only if all of that checks out.

P0571 code symptoms

• Check engine light on.
• Brake lights or cruise control that do not work correctly.
• Brake lights that are always on or that do not come on.
• Cruise control that does not engage.
• The shift lever will not come out of Park.

Likely causes of the P0571 code

1. Damaged or corroded connector. The most common cause.
2. Cut or shorted wiring between the switch and the computer.
3. Failed switch, open or internally shorted.
4. Missing power reference. Check whether other sensors also fail.
5. Computer. Uncommon, so rule out everything above first.

How to diagnose the P0571 code step by step

1. Read the switch value on the scan tool and compare it with what you expect.
2. Inspect the connector for corrosion, water or loose pins.
3. Check power and ground with the key on: correct reference and less than 0.1 V of drop on the ground.
4. Measure the signal with the connector plugged in and see whether it changes with the condition.
5. Do a wiring wiggle test with the scan tool in graph mode.
6. Check the continuity of each wire to the computer (less than 1 ohm).
7. Ask someone to watch the brake lights while you press the pedal.
8. Check the rubber stop on the pedal.

How to fix the P0571 code

• Repair the connector or the wiring.
• Replace the switch if the tests confirm it is bad.
• Correct the real condition if there is one.
• Clear the codes and verify with a road test.

Technical reference data

• Switch with 12 V when the pedal is pressed (brake lights) and often a second contact that opens when the pedal is pressed.
• Reference values only: check the manufacturer data for your vehicle.

Brand-specific notes

This is very common on Ford, GM, Nissan and Hyundai vehicles. On some Hyundai and Kia models there were campaigns for this switch.

P0571 on Ford

The brake switch circuit fault is very common on Ford vehicles.

P0571 on GM

The brake switch circuit fault is very common on GM vehicles.

P0571 on Nissan

The brake switch circuit fault is very common on Nissan vehicles.

P0571 on Hyundai

The brake switch circuit fault is very common on Hyundai vehicles, and on some Hyundai and Kia models there were campaigns for this switch.

Frequently asked questions about P0571