P0571
PowertrainCruise Control/Brake Switch A Circuit Malfunction
The ECU has spotted a dodgy signal from the brake switch, the little switch behind the brake pedal that tells the car when you're braking and drops the cruise control out. Most of the time you'll notice it because the cruise won't set, or it sets but won't cancel properly when you dab the brake. The thing to watch for is that this same switch usually runs your brake lights too, so a fault here can mean your brake lights play up, which turns a minor electrical niggle into something that gets you a pull from the police or fails an MOT.
ⓘ Information only. This page provides general educational information about fault code P0571. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0571 mean?
P0571 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cruise Control/Brake Switch A Circuit Malfunction.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on the dash, sometimes the only thing you'll see
- • Cruise control refuses to engage, or worse, won't drop out when you press the brake
- • Set, Resume and Accelerate buttons behave oddly or do nothing at all
- • Brake lights not coming on, or staying lit permanently even with your foot off the pedal
- • Automatic cars may refuse to shift out of Park (the shift interlock uses this same brake signal)
- • Traction or stability control warning lamps lighting up on some models
Possible causes
Causes commonly associated with P0571, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Faulty or knocked-out-of-position brake light switch on the pedal bracket. These are plastic and wear out, and a slightly mis-set one throws the code straight away
- 2. Corroded, chafed or broken wiring in the brake switch circuit, often where the loom flexes near the pedal box
- 3. Loose or damp connector at the switch, particularly on cars that have had a leaky bulkhead or footwell water
- 4. Blown fuse feeding the brake switch or cruise circuit
- 5. Cruise control buttons on the steering wheel gone faulty, classically after someone's spilt a drink down them
- 6. Internal fault in the body or powertrain control module, but that's rare and the last thing to suspect
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Scan the car and read off everything stored, not just P0571. A P0504 or a P0571 paired with P0572 or P0573 tells you a lot about whether it's the switch or the circuit
- 2. Get under the dash and look at the brake switch on the pedal bracket. Check it's clipped in square and not pushed out of adjustment, then wiggle the connector while watching live data
- 3. Check the relevant fuse, then trace the wiring and connectors for green corrosion, chafing or signs of water sitting in the footwell
- 4. Put a multimeter across the switch and confirm it makes and breaks cleanly as you press and release the pedal. A switch that's intermittent or sticking is your answer
- 5. Have a look at the steering wheel cruise switches if everything at the pedal checks out, especially if there's any history of a spill
Common questions about P0571
How quickly do I need to sort this out? +
Don't sit on it. The car will usually still drive fine and you can do short journeys, but if the brake light side of the switch is the bit playing up, your brake lights might not work. That's the part that matters. Driving around with no brake lights means the car behind you has no warning you're slowing, and it's an instant MOT failure and a chat with the police if you're caught. Check your brake lights work before you go anywhere, and if they don't, fix it before driving.
Is it the switch itself or just the wiring and plug? +
Usually the switch. They're a cheap plastic part that wears, and a knock or a bad adjustment is the most common cause by a mile. That said, on cars where water has got into the footwell or the loom has rubbed through near the pedal box, the wiring or connector is the real culprit and a new switch won't cure it. Test the switch on a meter first. If it checks out fine, start chasing the wiring back from the connector.
How long is this in the garage for? +
A straight switch replacement is quick, often under an hour including resetting and a road test, so you're looking at low three-figure labour at an independent plus a cheap part. If it turns into a wiring fault that needs tracing and repairing, that takes a lot longer and the bill climbs into mid three figures because diagnostic time is what costs. Module faults are rarer and dearer again, but you'd want that confirmed properly before agreeing to it.
Can I fit a cheap aftermarket switch or should I stick to OEM? +
For the brake switch a decent quality aftermarket part is fine and most motor factors stock them for a few pounds. Where you want to be careful is the absolute cheapest no-name eBay switches, because a poor one can stick or read intermittently and you'll be back doing the job again in a few months. Buy a known brand or genuine for the sake of a couple of quid. It's the labour and the brake light risk that make a repeat job annoying, not the part price.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →