Demystifying the P0571 Error Code: Causes, Symptoms, and Solutions
If you're a car owner, there's nothing more concerning than seeing that check engine light illuminate on your dashboard. One of the error codes that might be behind that glowing light is P0571. In this guide, we'll delve into what the P0571 code means, what causes it, the symptoms to look out for, and how you can address it. And if you're in the market for a reliable diagnostic tool to help you with this and other car issues, the iCarsoft CR MAX might just be the solution you need.
What is the P0571 Error Code?
The P0571 error code is a generic OBD-II diagnostic trouble code defined as "Cruise Control/Brake Switch A Circuit Malfunction". When your vehicle's Powertrain Control Module (PCM) detects an abnormal voltage or resistance in the cruise control/brake switch "A" circuit, it sets this code.
Key details to understand:
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The "A" in the code typically refers to a specific wire, connector, or harness within the circuit—but its exact definition varies by vehicle make and model. Always consult your vehicle’s service manual for precise, brand-specific details.
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The brake switch "A" is a critical link between the brake pedal and PCM: when you press the brake, it sends a signal to disengage cruise control (preventing acceleration while braking) and activate brake lights.
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P0571 is not vehicle-specific—it affects all makes and models with OBD-II systems, but is most commonly reported in vehicles with electronic cruise control (e.g., Ford, Toyota, Chevrolet, BMW).
Common Causes of the P0571 Code
P0571 stems from issues that disrupt the electrical signal in the cruise control/brake switch "A" circuit. Below are the most frequent culprits, ordered by likelihood:
Faulty Brake Switch
The top cause: A defective brake switch fails to send accurate signals to the PCM. Signs of failure include brake lights not turning on when the pedal is pressed, or cruise control refusing to disengage when braking. Internal wear (e.g., broken contacts) or mechanical misalignment (from pedal damage) often causes this.
Wiring Issues
Damaged, corroded, or frayed wires in the cruise control/brake switch circuit disrupt electrical flow. Common causes include wear and tear over time, exposure to moisture (e.g., engine bay leaks), or rodent damage. Loose connectors or broken wires create open/short circuits, triggering P0571.
Defective Cruise Control Switch
A faulty cruise control switch (on the steering wheel or dashboard) can disrupt the circuit. Stuck buttons, broken internal contacts, or poor electrical connection prevent the switch from communicating properly with the PCM, leading to code activation.
PCM Malfunction (Rare)
Internal PCM issues (e.g., damaged circuit boards, outdated firmware) rarely cause P0571—but they’re possible. The PCM may incorrectly interpret normal signals as "malfunctions" if its internal sensors or wiring fail. This is only likely after ruling out all other causes.
Symptoms Associated with P0571
P0571 symptoms directly impact safety and convenience—watch for these warning signs:
Illuminated Check Engine Light
The most obvious symptom: The PCM triggers the check engine light as soon as it detects an abnormal circuit signal. The light may be steady (minor issue) or flashing (rare, but indicates immediate circuit failure).
Inoperative or Erratic Cruise Control
Cruise control may refuse to engage, disengage unexpectedly while driving, or fail to respond to speed adjustments (e.g., "Set," "Resume," "Accelerate" functions). This is the PCM’s way of protecting you from unsafe cruise control operation.
Brake Lights Not Functioning
A critical safety risk: A faulty brake switch (linked to P0571) often prevents brake lights from turning on when the pedal is pressed. This makes it impossible for other drivers to anticipate your stops, increasing collision risk.
Unexpected Cruise Control Disengagement
Even if cruise control engages, it may shut off randomly—this happens when the PCM receives inconsistent signals from the brake switch circuit, prioritizing safety over functionality.
How to Diagnose and Fix P0571 (with iCarsoft CR MAX)
Pinpointing and resolving P0571 requires testing the circuit, switch, and wiring—tasks made simple with the iCarsoft CR MAX. Follow this step-by-step process:
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Read Codes and Freeze-Frame Data with CR MAX
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Connect the CR MAX to your vehicle’s OBD-II port (under the dashboard), power it on, and use AutoVIN Recognition to automatically identify your make/model (saves time vs. manual selection).
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Navigate to Engine Control Module > Fault Codes > Read Codes to confirm P0571. Check for related codes (e.g., P0572 for "Brake Switch A Circuit Low," P0560 for "System Voltage Malfunction") to rule out additional issues.
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Review freeze-frame data to see when the code triggered (e.g., "Cruise Control Active," "Brake Pedal Pressed")—this reveals if the problem occurs under specific conditions.
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Inspect the Brake Switch (with CR MAX Guidance)
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Use the CR MAX’s Component Location feature to find the brake switch (typically mounted on the brake pedal arm, near the firewall). This avoids guesswork about where to look.
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Visually inspect the switch for damage (cracks, loose mounting bolts) or misalignment (ensure it contacts the brake pedal when released).
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Test the switch with the CR MAX’s built-in Multimeter:
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Disconnect the switch connector and measure resistance (OEM specs vary, but most brake switches show 0Ω when pressed, ∞ when released).
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If resistance is outside the normal range, the switch is faulty and needs replacement.
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Check Wiring and Connectors
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Use the CR MAX’s Wiring Diagrams to trace the cruise control/brake switch "A" circuit (shows wire colors and connector locations).
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Inspect wires for fraying, cuts, or corrosion. Spray corroded connectors with electrical contact cleaner to remove dirt/debris.
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Test for continuity with the CR MAX’s Continuity Test: A "beep" indicates a solid connection; no beep means a broken wire (repair or replace with matching-gauge wire).
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Test the Cruise Control Switch
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Use the CR MAX’s Bi-Directional Testing to activate the cruise control switch remotely:
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Navigate to Special Functions > Cruise Control > Switch Test and trigger "Set," "Resume," and "Cancel" functions.
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If the PCM doesn’t register the switch inputs (check live data), the cruise control switch is defective and needs replacement.
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Address PCM Issues (If Needed)
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If the brake switch, wiring, and cruise control switch pass tests, use the CR MAX’s TSB Lookup (Technical Service Bulletins) to check for PCM firmware updates—outdated software often causes false P0571 codes.
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For internal PCM faults, consult a professional mechanic: They have specialized tools to reflash or repair the PCM (DIY PCM work is not recommended).
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Verify Repairs with CR MAX
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Use the CR MAX to Clear Codes from the PCM.
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Test drive for 20–30 miles: Engage cruise control, press the brake to disengage, and check if brake lights work.
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Re-scan the engine system. If P0571 does not return, the repair is successful. If it reappears, revisit wiring or switch connections.
Can I Drive with a P0571 Code?
While your vehicle will typically remain drivable with P0571, you should address the issue promptly for these reasons:
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Safety Risks: Inoperative brake lights make it impossible for other drivers to see when you’re braking—this significantly increases collision risk, especially in heavy traffic or at night.
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Cruise Control Failure: Without functional cruise control, long drives become tiring, and you may accidentally exceed speed limits (a safety and legal hazard).
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Emissions Testing: An illuminated check engine light (triggered by P0571) will cause your vehicle to fail emissions tests in most regions (e.g., California, EU countries).
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Escalating Damage: A minor wiring issue or faulty switch can lead to more costly repairs (e.g., PCM damage) if left unaddressed.
When to Seek Professional Help?
DIY repairs work for most P0571 cases (e.g., replacing a brake switch or fixing wiring), but consult a professional mechanic if:
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You’ve tested the brake switch, wiring, and cruise control switch with the CR MAX, but P0571 still reappears (likely a PCM issue).
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You’re uncomfortable working with electrical systems (e.g., soldering wires, testing circuits)—mistakes can cause short circuits or fire risks.
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Your vehicle requires specialized PCM reflashing (most dealers or certified shops have the tools for this).
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You notice additional symptoms (e.g., stalling, loss of power)—these may indicate unrelated issues that need professional diagnosis.
FAQ: Common Questions About P0571
Q: How much does it cost to fix P0571?
A: Costs vary by cause:
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Brake switch replacement: $30–$150 (DIY with CR MAX; $100–$250 at a shop).
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Wiring repair: $20–$100 (DIY; $100–$300 at a shop, depending on wire access).
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Cruise control switch replacement: $50–$200 (DIY; $150–$350 at a shop).
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PCM repair/reflash: $300–$1,000 (professional only, due to specialized tools).
Q: Will replacing the brake switch always fix P0571?
A: No—while it’s the most common fix, P0571 can also stem from wiring or cruise control switch issues. Always test the brake switch with the CR MAX’s multimeter first to confirm it’s faulty. If the switch passes the test, move to wiring inspection.
Q: Can a dead battery cause P0571?
A: Indirectly—low battery voltage (e.g., <12V) can disrupt PCM signal interpretation, leading to a temporary P0571 code. However, the code should clear after recharging the battery and resetting codes with the CR MAX. If it returns, the issue is not battery-related.
Q: Does the CR MAX work for P0571 on European vehicles (e.g., BMW, Mercedes)?
A: Yes—the CR MAX includes brand-specific diagnostics for European, Asian, and American vehicles. It can read P0571, access brake switch wiring diagrams, and run bi-directional tests on European models, which basic scanners often fail to support.
Q: How long does it take to fix P0571?
A: DIY repairs take 30–90 minutes (with the CR MAX):
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Brake switch replacement: 30 minutes (easy access on most vehicles).
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Wiring repair: 60–90 minutes (varies by wire location).
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Professional repairs take 1–2 hours (includes diagnosis and labor).
Summary Table: P0571 Diagnosis & Repair Steps
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Step
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Action with iCarsoft CR MAX
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Common Fix
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1
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Read P0571 + related codes; check freeze-frame data
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Confirm circuit malfunction; rule out other issues
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2
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Locate brake switch via Component Location; test resistance with multimeter
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Replace faulty brake switch
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3
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Trace wiring with diagrams; test continuity
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Repair/replace damaged wires or corroded connectors
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4
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Run bi-directional test on cruise control switch
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Replace defective cruise control switch
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5
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Clear codes; test drive + re-scan
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Confirm repair success; ensure no recurring P0571
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Conclusion
The P0571 error code (Cruise Control/Brake Switch A Circuit Malfunction) may seem like a minor inconvenience, but it poses safety risks (e.g., inoperative brake lights) and can escalate into costlier repairs. With the right knowledge and tools—like the iCarsoft CR MAX—you can diagnose and fix most P0571 cases yourself, saving time and money on shop visits.
Remember: Start with code reading and freeze-frame data (via CR MAX), then test the brake switch, wiring, and cruise control switch. If DIY steps don’t work, consult a professional for PCM-related issues. By addressing P0571 promptly, you’ll restore cruise control functionality, ensure brake lights work, and keep your vehicle safe on the road.
For reliable, professional-grade diagnostics for P0571 and hundreds of other codes, the iCarsoft CR MAX is a valuable addition to any car owner’s toolkit. Its multi-brand support, bi-directional testing, and built-in tools make it easier than ever to keep your vehicle running smoothly.
