Quick Answer
The P0571 code means Cruise Control/Brake Switch A Circuit Malfunction. The controller has detected an unexpected condition in the named brake-switch circuit. Check the actual brake lamps first, then compare supported pedal and switch data with the physical pedal position. Working lamps do not prove every switch contact or control-module signal is correct. Verify installation, adjustment, supply, connectors, and wiring before replacing a part.
What Does the P0571 Code Mean?
The brake-pedal signal serves more than the rear lamps. Depending on the vehicle, modules use it for cruise cancellation, engine or transmission control, starting interlocks, and other functions. P0571 identifies a problem in the specified switch A circuit or its expected behavior. The full OEM wording and the module reporting it determine the correct diagnostic path.
Some brake switches contain multiple contacts; other vehicles use electronic pedal sensors and module-mediated lamp control. A lamp can work while another contact, signal path, or plausibility check fails. Conversely, faulty lamp wiring can coexist with a valid pedal signal in one module. Compare both physical operation and the relevant reported states.
The label A is not a universal wire color, connector pin, or position on the pedal. Locate the component and circuits using the exact VIN, engine, and brake-system information. Do not assume that a switch advertised for a similar vehicle has the correct contact arrangement, adjustment method, or installation procedure.
Porsche Technical Information 39/12 ENU 9436, dated May 24, 2012, illustrates the importance of adjustment. For its specified 911 Carrera/Boxster 9x1 applications with P0571, Porsche directs technicians to check and document the brake-light switch adjustment before other work. The bulletin’s broader model list and procedures must not be applied as a universal adjustment instruction.
Different brake and communication codes need distinct checks
| Code | General description | Key distinction |
|---|---|---|
| P0571 | Cruise control/brake switch A circuit malfunction | Evaluate the named circuit and its expected states. |
| P0703 | Brake switch B circuit on applicable vehicles | Confirm the separate OEM circuit and module. |
| P0504 | Brake switch A/B correlation | Compare the required relationship between signals. |
| U0401 | Invalid ECM/PCM data received | Identify the receiving module and source-data issue. |
Check both sides of the evidence: Record lamp operation with the pedal released and applied, and compare it with supported switch or pedal PIDs. Neither a click from the switch nor one normal lamp proves the entire circuit.
P0571 Symptoms and Likely Causes
Common complaints include a warning lamp, cruise control that will not set or cancel normally, and brake lamps that stay on or fail to illuminate. Starting or shift-interlock behavior can also be affected on particular vehicles. Do not attribute a physical braking defect to a switch code without a separate safety assessment.
A switch adjustment, pedal-return, circuit, or lamp-control problem may be present.
Treat missing brake-lamp operation as a safety problem before a road test.
The system may reject an implausible pedal state or disable cruise until diagnosis.
Engine, stability, starting, or gear-selection behavior can depend on the applicable signal path.
Practical cause-checking order
- Switch fit or adjustment: Incorrect installation, a disturbed bracket, or a self-adjusting mechanism handled incorrectly can cause an unexpected state.
- Pedal-return or stop issues: Inspect the correct mechanical contact point, stopper where fitted, obstruction, and return behavior without changing pedal geometry.
- Feed, connector, or wiring faults: A fuse, loose terminal, corrosion, open, or short can affect the switch or lamp circuit. Inspect recent repairs and accessories.
- Internal switch or signal faults: A failed contact or sensor is possible after installation and external circuits are checked. Module faults require separate supporting tests.
Do not change pedal stops, bypass the switch, or perform an ECU factory reset to hide the code. Use only the vehicle-specific adjustment and replacement procedure; incorrect work can leave brake lamps or cruise cancellation unsafe.
How Serious Is P0571, and Can You Drive?
Before deciding to drive, verify actual brake-lamp operation and assess braking, pedal return, and gear selection. A steady engine light with otherwise normal operation still needs prompt diagnosis. Avoid using cruise control while its brake-cancellation signal is unresolved.
Do not road-test a vehicle with missing or continuously illuminated brake lamps, unsafe braking, unpredictable pedal behavior, or an unsafe interlock complaint. Arrange qualified repair or recovery. A code that looks minor can affect how other drivers see your braking and how the vehicle interprets pedal input.
Stop and arrange a tow for brake lamps that do not operate correctly, impaired braking, a pedal that does not return normally, or unsafe cruise/gear-selection behavior. Diagnose in a secured stationary setting before any road test.
Secure the vehicle against movement while inspecting under the dashboard. Keep clear of pedals and moving linkage during tests. Do not probe unidentified safety-system wiring or disturb airbag circuits. Brake adjustment and electrical work should follow current service information and be handled by a qualified technician where needed.
How to Diagnose P0571 in the Right Order
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Check actual lamps and save the full scan
With the vehicle secured, have a helper observe every brake lamp while the pedal is released and applied. Record lamps that remain on, fail to light, or behave inconsistently. Confirm whether an accessory or trailer connection is affecting lamp behavior before assuming the pedal switch is responsible.
Save the complete P0571 record, reporting module, suffix, status, and available freeze-frame information. Scan relevant engine, brake, body, and transmission modules. Preserve correlation, supply, communication, and interlock faults before clearing so the diagnosis reflects the original complaint.
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Inspect pedal return and switch installation
Identify the specified switch or pedal sensor and inspect its bracket, mounting, lock, contact point, and connector. Check for an obstruction or a damaged pedal stopper where fitted. Review recent switch, brake, dashboard, or accessory work that may have disturbed installation.
Use the manufacturer’s adjustment procedure rather than setting an arbitrary gap. Some switches are self-adjusting and can be damaged by handling them incorrectly. Do not alter pedal height, travel, or stop position to make a scan PID change. Check applicable bulletins before replacing a functioning component.
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Compare supported pedal and switch states
On a supported vehicle, observe the required brake-switch, pedal, or stop-lamp PIDs in the relevant modules. Compare released and applied states with actual lamp operation. If the system uses multiple contacts, check the expected relationship between them according to the service information.
Look for a state that sticks, changes intermittently, or disagrees between modules. The scanner label and signal polarity matter: an ON or OFF value is not meaningful without knowing what it represents. Do not assume a generic engine PID proves the body module’s lamp command or a separate cruise contact is correct.
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Verify supplies, grounds, connectors, and harness
Use the correct wiring diagram to identify the switch feeds, grounds where used, outputs, fuses, and module connections. Inspect terminal fit, corrosion, loose locks, chafing, and previous repairs. A recently installed accessory or trailer harness may need investigation if it affects the relevant circuit.
Measure the required feeds and signal states with suitable equipment in the specified operating conditions. Use voltage-drop or loaded checks where instructed. Do not replace a blown fuse without finding why it opened, and never bridge a protective circuit or apply battery voltage to an unidentified module signal.
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Test the component and isolate the failed path
Follow the OEM continuity, voltage, or sensor-signal test for the actual switch design. Test the correct contacts with the circuit isolated when instructed. Mechanical switch testing differs from evaluating an electronic pedal sensor; a generic continuity rule does not cover both.
Compare measurements at the switch and receiving module to distinguish a component defect from a harness problem where the procedure permits. If the physical switch signal is correct but module data is wrong, continue the specified circuit and module checks. Do not condemn a controller merely because one PID appears unexpected.
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Repair, adjust correctly, and verify safety
Repair the proven connector, harness, feed, mechanical contact, or switch defect. Install and adjust a replacement exactly as specified and complete any required initialization. Restore trim and wiring without creating a pedal obstruction. Code clearance comes after repair, not as a substitute for it.
Verify all brake lamps, released and applied pedal states, starting and shift-interlock behavior where applicable, and the absence of current or pending faults. Confirm safe cruise cancellation only by the prescribed test after stationary safety checks pass. Do not use normal public-road traffic to experiment with an uncertain brake signal.
Specifications are vehicle-specific. Switch gaps, contact logic, circuit voltage, adjustment steps, and initialization requirements vary by vehicle. The Porsche example is limited to its defined applications. Use current VIN-specific instructions rather than a universal plunger setting or an ECU reset routine.
P0571 Repairs and Typical Costs
A confirmed repair may be correct switch installation or adjustment, restoration of a pedal contact point where fitted, wiring or connector repair, or replacement of a switch with a proven internal defect. Record the failed test and verify the safety function after the work.
Reduced cruise use or avoiding hard braking is not a repair or an evidence-based prevention method for a circuit fault. Maintain correct mounting and routing, address water or wiring damage, and follow the manufacturer’s procedures. A software action needs a matching OEM instruction, not a general promise that a reset fixes P0571.
| Possible path | Current US estimate |
|---|---|
| Lamp, pedal-signal, and circuit diagnosis | Local diagnostic quote |
| Correct switch installation or adjustment | Vehicle-specific labor quote |
| Confirmed switch or connector replacement | Part and access quote by VIN |
| Harness or separately proven module repair | Quote after the failed path is isolated |
The estimate should distinguish a simple adjustment from a new switch, wiring work, or a separate brake-system repair. Ask which lamp and PID checks failed and whether the quoted work includes installation, any required setup, and final safety verification.
Access under the dashboard and switch design can affect labor. Confirm warranty or campaign eligibility using the VIN. A code-only price range cannot establish the needed repair.
Using iCarsoft CR MAX for P0571
On a supported vehicle, iCarsoft CR MAX can help save full-system fault records and view available brake-switch or pedal-state data. Comparing relevant modules can help separate a local switch problem from a signal or communication issue.
Confirm exact vehicle, model year, module, software, and PID coverage before purchase. A generic brake-switch parameter may not expose every contact or signal used by the vehicle. General full-system capability does not guarantee an individual adjustment, initialization, or active-test routine.
Save evidence before choosing a repair
iCarsoft CR MAX
Compare supported brake-pedal and module data with actual lamp behavior, then verify the physical switch and wiring using the OEM procedure.
Check current CR MAX price and availabilityCheck CR MAX compatibility by VINUse a supported service function only when the manufacturer calls for it and the vehicle is safely secured. Do not command unrelated ABS or brake actuators merely to diagnose a pedal-switch code. OEM-specific programming or adjustment equipment may be required for a particular application.
Know the measurement boundary. A scanner does not directly measure switch contact resistance, connector voltage, terminal fit, pedal adjustment, or actual brake-lamp illumination. Use visual checks and appropriate electrical equipment alongside the reported data.
Verify the P0571 Repair
Confirm every brake lamp switches off and on correctly, the pedal returns freely, and the reported states agree with the expected logic. Recheck connector engagement, trim clearance, starting, and gear-selection interlocks where relevant. Preserve the completed scan and the original failed-test evidence.
Clear eligible codes as instructed, repeat the relevant conditions safely, and rescan the reporting modules. Verify that current and pending P0571 do not return. A light that stays off immediately after erasing codes does not establish safe brake-signal operation.
A permanent P0571 can remain immediately after a successful repair. If the vehicle stores it as a permanent DTC, a scan tool or battery disconnect cannot erase it. Once current and pending faults are absent, the OBD system removes the permanent record only after the applicable monitor reruns and passes.
Related Brake Switch and Module Signals Code Guides
P0571 Frequently Asked Questions
Can the brake lamps work and still have P0571?
Yes. Some switches have multiple contacts and some vehicles distribute pedal information through modules. Normal lamp operation does not prove that every cruise, engine, or correlation signal is valid. Compare the required PIDs and circuit measurements.
Should I replace the brake switch immediately?
First check installation, adjustment, pedal return, supply, connectors, and wiring. Replace the switch when its failure is supported by testing. A correctly functioning component can produce a complaint if it is installed or adjusted incorrectly.
Can I drive if the brake lamps stay on?
Do not road-test until brake-lamp operation is restored. Continuously lit lamps can prevent other drivers from recognizing braking. Missing lamps, unsafe braking, or abnormal pedal return also require repair or recovery before driving.
Does resetting the ECU fix P0571?
A reset does not repair a broken wire, faulty contact, or incorrect adjustment. Save the evidence and correct the confirmed defect first. Follow only the initialization or code-clearance procedure specified for the repair.
Does the Porsche adjustment bulletin apply to my car?
Only if the model, complaint, and code conditions match its scope. The cited P0571 instruction concerns specified 911 Carrera and Boxster 9x1 applications. Use the current workshop procedure and verify applicability by VIN.
Will avoiding cruise control prevent the code?
No general prevention claim follows from P0571. Avoid cruise while its brake-cancellation signal is unresolved, but diagnose the electrical or installation defect. Less frequent cruise use does not repair the monitored circuit.
Technical and cost references
Product information: Official iCarsoft CR MAX page.
Editorial note: Use current manufacturer instructions for your VIN and qualified help for work beyond your training. A code identifies a test result, not a confirmed failed part.
