OBD-II trouble code
P0571: Cruise Control / Brake Switch "A" Circuit
Almost every brake pedal switch is two switches in one housing that move in opposite directions, and this code is the module reporting that it cannot make sense of the pair. Your brake lights can be completely normal while it is stored.
Quick facts
- System
- Powertrain
- Category
- Cruise Control
- Severity
- Low severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $0 – $320
- DIY difficulty
- Intermediate DIY
What does P0571 mean?
P0571 names the cruise control and brake switch "A" circuit generally, without saying whether the reading was too high or too low. That vagueness is not the module being unhelpful. It is the module reporting a different class of problem from its low and high siblings: not a voltage outside a window, but a switch whose behaviour does not add up.
To see why that matters you have to know what a brake pedal switch actually is. It is almost never a single switch. In one plastic housing, sharing one spring-loaded plunger, sit two or sometimes three electrically independent contact sets, and they are deliberately built to move in opposite directions. One closes when the pedal goes down. Another opens at the same instant. They have separate wires, they go to separate places, and nothing electrically connects them inside the switch except the plastic plunger they all ride on.
That design exists for one reason: it lets a control module verify the pedal instead of merely reading it. Two contacts that always disagree in a known pattern give the module a way to catch a switch that has failed in a way a single contact could never reveal. A single contact that sticks closed just looks like a driver with a foot on the brake, which is a perfectly ordinary thing. Two contacts that both say the pedal is pressed cannot both be right, and that is what the module is set up to notice.
The consequence catches a lot of people out, and it is the single most useful thing on this page. The contact that lights your brake lamps and the contact that talks to the powertrain module are different pieces of metal. Either one can fail while the other continues working perfectly. So this code very commonly appears on a vehicle whose brake lights are flawless — you press the pedal, the lamps come on, the lamps go off, everything looks right, and the module is still storing a fault, because the contact it watches is not the contact the lamps use. Concluding that the switch must be fine because the lamps are fine is the wrong conclusion, and it is the reason these get misdiagnosed as wiring or module faults.
One more thing worth settling early. The letter "A" in the title is a designator, not a description. Some vehicles genuinely fit two separate brake switch devices — a primary and a redundant — and on those, "A" identifies which physical part is being reported. On most vehicles "A" is simply the first and only brake switch. Find out which arrangement you have in service data before ordering anything, because on the two-device designs the wrong part is a complete waste of an afternoon.
Common causes
- Failed striker pad or bumper on the pedal bracket, letting the switch plunger over-extend
- Internal wear in one contact set of a multi-contact brake switch, with the other set still working
- Switch that has migrated on its threads or ratchet mount since it was installed
- Contacts that change state at the wrong point in pedal travel relative to each other
- Bent or distorted pedal bracket after a heavy footwell impact or a previous repair
- Damaged or back-out terminal in the switch connector affecting one circuit only
- Splices left in the pedal-switch harness by trailer, alarm or remote-start installations
- Wrong replacement switch fitted — a lamp-only unit substituted for a multi-contact one
Symptoms
- Check engine light with brake lights that work completely normally
- Cruise control unavailable or dropping out with no other obvious fault
- Occasional refusal to shift out of park, clearing after a second attempt
- A brake switch correlation code stored at the same time
- Transmission shift feel changing on light braking
- Fault first appearing after pedal, steering column or under-dash work
- Engine running and idling exactly as it always has
- Fault appears and disappears rather than staying set
Diagnostic steps
- 1.Before anything electrical, get the striker pad in front of you. On a large number of vehicles the switch plunger does not rest against the metal pedal arm — it rests against a small moulded pad clipped or glued to the pedal bracket. That pad ages, cracks and drops out. When it does, the plunger extends further than it was ever meant to and the switch reports the pedal as pressed with your foot nowhere near it. The part costs a few dollars. Look for it on the floor mat.
- 2.Identify how many contacts your switch has and what each one feeds. Pull the connector and count the cavities. A two-wire switch is a lamp switch only. Four or six wires means two or three independent contact sets sharing one plunger, and the one that reports to the powertrain module is usually not the one that lights the lamps.
- 3.Back-probe each contact set separately with the key on and read them together. At rest, a correctly built pair reads as one closed and one open. Press the pedal slowly and watch them change: they should swap state within a few millimetres of each other, and neither should hesitate, flicker or change twice.
- 4.Check the switch's position on its mounting. Threaded and ratcheting switches set their own depth against the pedal on installation and they migrate afterwards, particularly if the pedal has ever been leaned on hard. There should be a small amount of pedal travel before either contact changes state.
- 5.Compare what the scan tool says with what the pedal is doing. A live-data brake input that agrees with your foot on every press does not clear this code — the fault may be in the second contact, which the generic data list often does not show. If your tool only displays one brake parameter, you are seeing half the switch.
- 6.Only after the switch has been proven should you go looking in the harness. Inspect where the pedal-switch leads pass the edge of the bracket and where they join the main under-dash loom, and look for repair splices left behind by a previous trailer, alarm or remote-start installation.
Repair cost
$0 – $320
The floor is genuinely zero because a meaningful share of these are a pedal striker pad that has fallen out, and the pad is a few dollars or can be substituted with the correct replacement bumper from a dealer parts counter for under $10. A complete brake switch is $15 to $70 for the part and typically thirty minutes under the dash, which puts a full repair around $80 to $200 at a shop. Diagnosis is $80 to $150 and is worth paying for here, because the specific failure this code describes is invisible from the driver's seat and gets misattributed to wiring more often than any other brake switch fault. Costs run to the upper end on vehicles that fit two separate brake switch devices, where the correct one has to be identified before it is ordered.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with brake light switch replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.