OBD-II Code P1571: Brake Switch Circuit Malfunction

What Does P1571 Mean?

P1571 is a manufacturer-specific code, meaning its definition changes depending on your car. Most commonly, it indicates a problem with the brake light switch circuit. Your car's main computer (PCM) detects an illogical signal from the switch that monitors brake pedal position. On many GM vehicles, it specifically points to a communication failure between the traction control module and the PCM. For Subaru, it indicates a security immobilizer problem that prevents the engine from starting. For Volkswagen/Audi, it points to a short in the left engine mount solenoid valve circuit.

Technical definition: The official SAE/OBD-II definition for P1571 varies significantly by manufacturer. Common definitions include: Brake Switch Malfunction (Ford, Peugeot, Jaguar, Kia); Traction Control Torque Request Circuit (GM, Oldsmobile); Left Engine Mount Solenoid Valve Short to B+ (Volkswagen/Audi); Reference Code Incompatibility (Subaru); Lost Communications With Steering Angle Sensor (Toyota); and ECU Hardware Malfunction (Nissan).

Can I Drive With P1571?

Yes, But With Caution. Driving is possible but not recommended and should be limited to getting to a repair shop. Critical safety features like cruise control, traction control, and anti-lock brakes (ABS) are disabled. Most importantly, your brake lights often fail or stick on, creating a significant risk of a rear-end collision. On some vehicles, you cannot shift out of park, leaving you stranded. On Jaguars, the electronic park brake is also inoperative.

Common Causes

• Defective Brake Light Switch (Very Common) — The most frequent cause is a faulty brake light switch. This small, inexpensive sensor by the brake pedal wears out, gets stuck, or fails electronically, sending incorrect signals.
• Blown Fuse (Common) — A blown fuse in a related circuit (brake lights, ABS, or ECU) triggers this code. This is the easiest and cheapest problem to check.
• Wiring or Connector Issues (Common) — The wiring harness and connectors going to the brake switch or the ABS module become damaged, corroded, or loose. This interrupts the signal, causing the code. This includes poor ground connections for the EBCM or PCM.
• Faulty ABS/Traction Control Module (EBCM) (Less Common) — On GM vehicles, this code points to a communication failure between the Electronic Brake and Traction Control Module (EBCM) and the PCM. The module itself fails due to internal solder joint fractures from vibration and heat.
• Weak or Failing Battery (Less Common) — Low or unstable system voltage from a bad battery causes communication glitches between modules, indirectly triggering P1571 and other electronic codes, especially on sensitive European vehicles.
• Incorrectly Adjusted Brake Light Switch (Rare) — If the brake switch was recently replaced or disturbed, it is likely improperly adjusted. If it triggers too early or too late relative to pedal movement, the computer logs a fault.
• Mechanical Damage to Brake Pedal Assembly (Rare) — Physical damage to the brake pedal assembly or its mounting bracket prevents the brake light switch from activating properly.
• Faulty Powertrain Control Module (PCM) (Rare) — In rare instances, the vehicle's main computer is the source of the problem through a software glitch or hardware failure. This is the last item to diagnose.

Symptoms

• Check Engine Light is On — This is often the first and sometimes only indicator of a detected problem.
• Brake Lights Don't Work or Stay On — Your brake lights fail to illuminate when you press the pedal, or they stay on continuously, draining the battery and creating a major safety hazard.
• Cannot Shift Out of Park — Most automatic transmissions require a signal from the brake switch to release the shifter from 'Park'. A faulty switch leaves your car stuck.
• Cruise Control Does Not Work — The cruise control system disengages when you press the brake. If it receives a faulty signal, it disables itself as a safety precaution.
• ABS or Traction Control Warning Lights are On — Because the brake signal is critical for these systems, a fault disables them and illuminates their dashboard warning lights.
• Engine Will Not Start — On Subaru vehicles, this code indicates an immobilizer fault that prevents the engine from starting. On push-button start vehicles, a bad brake switch prevents the car from recognizing the pedal is pressed.
• Sluggish Acceleration or Reduced Engine Power — Some vehicles have a brake-throttle override system. If the brake switch sends a constant 'on' signal, the ECU limits engine power to prevent unintended acceleration.
• Erratic Brake Light Behavior (Flickering) — An intermittent failure in the switch or wiring causes the brake lights to flicker, confusing other drivers.
• Invalid PWM or Missing Signal (GM) (scan-tool only — no driver-felt sign) — On a scan tool, a technician sees the 'Traction Control Torque Request' signal is out of its normal 10-90% duty cycle range, or missing entirely.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Replace Brake Light Switch — Parts: $15-$90, Labor: $70-$120, ~0.8 hr book time (DIY)
• Replace Blown Fuse — Parts: $1-$5, Labor: $0-$50, ~0.1 hr book time (DIY)
• Repair Wiring or Connectors — Parts: $10-$60, Labor: $120-$250, ~1.5 hr book time (Intermediate)
• Repair ABS/EBCM Module — Parts: $150-$400 (for a mail-in repair service), Labor: $120-$180 (to remove and reinstall), ~1.2 hr book time (Professional)
• Replace ABS/EBCM Module — Parts: $700-$2,500, Labor: $120-$180, ~1.5 hr book time (Professional)
• Reset Immobilizer / Reprogram Keys (Subaru) — Parts: $0, Labor: $100-$200 (dealer service), ~1.0 hr book time (Professional)

DIY vs Professional

• Replace Brake Light Switch — Beginner:
  Tools: Basic hand tools (pliers, screwdriver, small socket set).
• Repair Wiring or Connectors — Beginner:
  Tools: Multimeter, wire strippers, crimpers, heat shrink, soldering iron (recommended).
• Repair/Replace ABS/EBCM Module — Beginner:
  Tools: Socket set, flare nut wrenches (for brake lines), scan tool with ABS bleeding function.
• Reset Immobilizer / Reprogram Keys (Subaru) — Beginner:
  Tools: Proprietary dealership diagnostic tool (e.g., Subaru Select Monitor).

Used vs. New Parts: Buying Guide

When a used part is worth it: For an expensive ABS/EBCM module, a used part from a reputable salvage yard offers significant savings ($50-$200 for used vs. $700+ new). This is a reasonable choice for older, high-mileage vehicles.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Match the part number exactly. For GM, ensure the donor vehicle had the same traction control options (e.g., JL4).
• Check for corrosion on the connectors and housing.
• Ask for a warranty, which is typically 30-90 days for used parts.

Decision logic:

• If The fault is a simple brake light switch. → Always buy new. The part is inexpensive ($15-$90) and a used one offers no reliability guarantee.
• If The fault is the ABS/EBCM module and a mail-in repair service is available. → Choose the mail-in repair service. It costs less than a new module, retains your vehicle's original programming, and is more reliable than a random used part.
• If The fault is the ABS/EBCM module and repair is not an option. → A used module is a budget-friendly choice, but it requires reprogramming to your vehicle's VIN at an additional cost.

Warranty tradeoff: Used parts typically have a 30-90 day warranty. Remanufactured or new aftermarket parts often carry a 1-year to lifetime warranty. OEM new parts have a 1-2 year warranty.

Worst-case if a used part fails: $300-$500 if a used ABS module is faulty or incompatible, requiring repeated labor for removal/installation and the cost of another part.

What Happens If You Wait — Timeline

1. Immediate: Code sets. Check Engine Light, ABS, and/or Traction Control lights illuminate. Cruise control is disabled. Brake lights are intermittent, stuck on, or completely inoperative. (MPG impact: 0%% · Added cost: $0 (but high safety risk))
2. 1-4 weeks: If brake lights stick on, a parasitic drain begins. The battery struggles to start the car. If brake lights are off, there is a high risk of a rear-end collision. Driving without ABS/TCS reduces stability. (MPG impact: 0-5% (if brake-throttle override is active)% · Added cost: $150-$300 for a new battery if drained completely multiple times.)
3. 1-6 months: For GM EBCM issues, continued thermal cycling causes initial hairline solder cracks to propagate, leading to frequent communication dropouts. For brake switch issues, the car becomes permanently stuck in Park. (MPG impact: 0-5%% · Added cost: $100-$250 for a tow if stranded.)
4. 6+ months: Ignoring a failing EBCM leads to complete and permanent module failure. The initial fault, which was repairable for $150-$250, now requires a full module replacement. (MPG impact: 0-5%% · Added cost: $800-$2500 for a new, programmed EBCM module.)

Cost of Not Fixing It

• Immediate: Safety hazard due to inoperative or constantly-on brake lights, significantly increasing the risk of a rear-end collision. Inability to shift out of Park leaves you stranded. (Added cost: Potential traffic ticket or cost of an accident deductible.)
• 0-3 months: If brake lights stick on, it causes a parasitic battery drain, requiring a jump-start or a new battery. Continued driving with disabled ABS/Traction Control reduces vehicle stability in emergency maneuvers. (Added cost: $150-$300 for a new battery if drained completely multiple times.)
• 3+ months: Ignoring a communication fault masks a more serious underlying issue with the ABS module. Driving with a faulty brake switch that limits engine power puts extra strain on the transmission. (Added cost: $800-$2500 for a new, programmed EBCM module.)

Diagnosis Steps

1. Verify Code and Check for Other Codes
   Use an OBD-II scanner to confirm P1571 is present. Check for any other codes, especially from the ABS or transmission modules (C-codes or U-codes), as they provide important clues about the specific manufacturer's definition and root cause.
   Tools: OBD-II Scanner (Beginner)
2. Check for Technical Service Bulletins (TSBs)
   Before diving into repairs, search for TSBs for your specific vehicle and this code. Manufacturers like GM and Jaguar have issued bulletins (e.g., GM #PI00219, Jaguar #SSM-71218) that identify known software glitches or specific communication issues that mimic a hardware fault.
   Tools: Internet access (Beginner)
3. Test the Brake Lights
   Have a friend stand behind the car while you press and release the brake pedal. Check if the brake lights function correctly. Flickering or non-working lights strongly suggest a bad switch or wiring.
   Tools: A friend (Beginner)
4. Inspect Fuses
   Check your vehicle's fuse box for any fuses related to the brake light system, ABS, or ECU. A simple blown fuse is often the root cause.
   Tools: Owner's manual, fuse puller or needle-nose pliers (Beginner)
5. Check Battery and Charging System
   Before replacing expensive modules, verify the battery is healthy and the alternator is charging correctly. With the engine running, system voltage must be stable between 13.5 and 14.5 volts. Low or fluctuating voltage causes a host of communication codes, including P1571.
   Tools: Multimeter or battery tester (Beginner)
6. Visually Inspect the Brake Light Switch
   Locate the brake light switch, typically mounted on a bracket near the top of the brake pedal arm. Look for obvious signs of damage, loose wiring, or a misaligned switch.
   Tools: Flashlight (Intermediate)
7. Brake Switch Continuity Test
   Disconnect the switch connector. Set a multimeter to the continuity (beep) or Ohms setting. For a typical 4-pin switch, one circuit shows continuity (near 0 Ω) only when the pedal is pressed, and the other circuit shows continuity only when the pedal is released. If the switch fails either test or shows infinite resistance (OL) in both states, it is defective.
   Tools: Multimeter (Advanced)
8. Brake Switch Voltage Test
   With the key on, probe the harness connector for the brake switch. One wire must have constant battery voltage (B+), typically 12.0-12.6V with the engine off. When the brake pedal is pressed, this voltage passes through the switch to the output wire that feeds the brake lights and control modules. Lack of B+ indicates a wiring or fuse issue upstream.
   Tools: Multimeter, Vehicle Wiring Diagram (Advanced)
9. Inspect ABS/EBCM Wiring and Connectors
   If the brake switch checks out (especially on a GM vehicle), inspect the wiring and main connector at the ABS or Electronic Brake Control Module (EBCM). Look for corrosion, bent pins, or damaged wires, which are common issues on modules mounted under the vehicle. Check the EBCM ground connection for low resistance (under 1.0 Ω) to the chassis.
   Tools: Flashlight, Socket Set, Multimeter (Advanced)
10. CAN Bus Network Voltage Analysis
    For communication-related definitions (GM, Jaguar, Toyota), a technician checks the CAN bus network. With the key on, using a multimeter, CAN High (CAN-H) reads ~2.5-3.5V and CAN Low (CAN-L) reads ~1.5-2.5V. With an oscilloscope, a healthy bus shows clean square waves. A flat line or voltages shorted to ground (0V) or power (5V/12V) indicate a network wiring fault or a failed module.
    Tools: Multimeter, Oscilloscope (Professional)
11. GM Torque Request Signal Analysis (Pro Tip)
    For the GM-specific P1571, the 'Traction Control Torque Request' signal is a Pulse-Width Modulated (PWM) signal. Using an oscilloscope, a technician probes this specific wire between the EBCM and PCM. A healthy signal is a square wave at a fixed frequency (e.g., 128 Hz) with a varying duty cycle. A flat line or noisy signal points to a wiring or EBCM fault.
    Tools: Oscilloscope, Wiring Diagram (Professional)
12. VW/Audi Engine Mount Solenoid Test
    For the VW/Audi definition, locate the left engine mount solenoid. Disconnect it and measure its internal resistance with a multimeter. A typical resistance value for a good solenoid is between 10 and 15 Ohms. A reading of infinity (OL) indicates an open circuit, while a reading near zero indicates a short.
    Tools: Multimeter, Repair Manual (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Vehicle Speed: 0 mph (When the fault is an inoperative brake switch, the code sets when the PCM expects a brake signal (e.g., to shift from park) but receives none.)
• Brake Pedal Status: Off/On (Mismatch) (The PCM detects a conflict, such as the vehicle decelerating while the brake switch signal remains 'Off', or accelerating while the signal is 'On'.)
• Engine RPM: 500-800 RPM (Idle) (For the GM variant, the communication fault between the EBCM and PCM is detected shortly after startup during the initial system self-checks at 500-800 RPM.)
• System Voltage: 13.5-14.5 V (The code typically sets during normal operating voltage (13.5-14.5V), which rules out a failing battery as the direct cause.)

Related Codes

• C1277 / P1689 (GM) — On GM vehicles, these codes confirm a communication breakdown. P1571 is the PCM reporting it didn't receive the 'torque request' signal from the EBCM. P1689 is the PCM reporting an issue with the 'delivered torque' signal. C1277 is the EBCM's code for the same fault.
• U0100 (Jaguar) — On Jaguar models, U0100 ('Lost Communication with ECM/PCM') alongside P1571-64 strongly indicates the software communication glitch described in TSB SSM-71218. Do not replace the brake switch if U0100 is present.
• P1572 (Subaru) — P1572 ('IMM Circuit Failure') often accompanies P1571. P1571 specifically means the security codes between the immobilizer and ECM do not match. P1572 indicates a general circuit failure in the communication line between them.
• C0298 (GM) — This EBCM code indicates the PCM cannot perform the requested torque reduction. If you have C0298 but not P1571, the issue is something else preventing torque reduction, like an engine overheat condition.

Climate & Environmental Factors

• High Humidity / Road Salt: Moisture penetrates connectors for the brake light switch and the ABS/EBCM module. This leads to pin corrosion, causing high resistance or open circuits that trigger P1571.
• Extreme Cold: Very cold temperatures make plastic components like the brake light switch brittle and prone to mechanical failure. Wiring insulation becomes stiff and cracks, increasing the risk of shorts.
• Extreme Heat: Sustained engine bay heat accelerates the degradation of electronic components. For GM vehicles, heat is a primary contributor to the internal solder joint fractures that cause EBCM communication failures.

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Required for Subaru immobilizer and complex Jaguar software faults; recommended for any repair involving module replacement and programming.
  Best for: Vehicles under warranty or with active recalls., Subaru immobilizer issues (requires proprietary tools)., Jaguar software-related faults (requires knowledge of TSBs)., Complex module programming (e.g., new GM EBCM).
  Downsides: Highest labor rates and part costs., May recommend replacing a whole assembly when a smaller component or wiring fix is possible. (Typical cost: +50% vs. baseline)
• Independent Shop: Best choice for straightforward brake switch replacements. A well-equipped independent handles GM EBCM wiring issues, but refers Subaru/Jaguar-specific problems to a dealer.
  Best for: Common brake switch failures (Ford, Kia, Hyundai)., Out-of-warranty vehicles with cost sensitivity., Diagnosing wiring or ground issues (for skilled electrical diagnosticians).
  Downsides: Quality and diagnostic skill vary greatly., May lack expensive manufacturer-specific tools for programming or immobilizer work. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID for diagnosis. Only use if you have already confirmed a simple brake switch is the fault and you need a low-cost parts replacement.
  Best for: Simple, pre-diagnosed brake switch replacement.
  Downsides: High risk of misdiagnosis due to the code's complexity., Technician skill is inconsistent; may lack experience with manufacturer-specific definitions of P1571., Likely to default to replacing the brake switch, which will not fix the issue on a GM, Subaru, or VW. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the car's private-party value, pause and consider your alternatives.

• Car worth $4000, fix is $250: Fix it. This is a low-cost repair for a simple brake switch, well below the threshold.
• Car worth $12000, fix is $1800: Borderline — get a 2nd opinion. This likely involves a module replacement. Explore mail-in repair services or warrantied used parts to lower the cost.
• Car worth $3000, fix is $1800: Walk away. The repair cost is over half the car's value. It is not economically sensible.

What Scan Tool You Need for This Code

Minimum: A scanner that reads Enhanced Codes from other modules like the ABS, BCM, and TCM. A basic engine-only code reader is not sufficient for P1571.

A $20 code reader only shows the P1571 from the engine computer. It does NOT see the related, critical codes from other modules, such as a C1277 from the ABS module on a GM or a U0100 on a Jaguar.

Budget: BlueDriver Pro / Autel AL619 (~$100) — Reads and clears codes from the engine, ABS, and airbag systems. This is the minimum needed to see if P1571 is accompanied by related ABS codes.

Mid-range: Foxwell NT510 Elite / Autel MaxiCOM MK808 (~$350) — Provides full-system diagnosis to read all modules, offers bidirectional control to test components, and performs service functions like ABS bleeding.

Professional: Autel MaxiSYS MS906 Pro / Launch X431 (~$1200+) — Offers full OEM-level diagnostics, module programming, and coding. Required for complex tasks like programming a new EBCM or re-synchronizing immobilizer modules.

Rent vs buy: AutoZone's free rental scanner is often a basic code reader that fails to read the necessary ABS or body codes. For P1571, it is a poor choice. If this is a one-time diagnosis, paying a shop for a proper diagnostic scan is better than buying the wrong tool.

How to Clear the Code After You Fix It

1. Use an OBD-II scan tool to erase the fault codes.
2. Perform a complete drive cycle to allow the vehicle's readiness monitors to run their self-tests.
3. Check for pending or current codes again after the drive cycle.

Drive cycle (~20 minutes): A general drive cycle involves a cold start (engine coolant below 122°F), a 2-3 minute idle, followed by 10-15 minutes of mixed city and highway driving (including steady cruising around 55 mph), and returning to a stop.

Readiness monitors affected: Comprehensive Component Monitor, Misfire Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Simply disconnecting the battery clears the code but resets all readiness monitors, causing an automatic emissions test failure.
• The code reappears immediately if the underlying mechanical or electrical fault is not repaired.
• For Subaru immobilizer issues, clearing the code fails; the modules must be reprogrammed by a dealer.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An active Check Engine Light is an automatic failure. After repair, you must complete a drive cycle to set the readiness monitors before re-testing.
• New York: Any fault that illuminates the Malfunction Indicator Lamp (MIL) results in an emissions inspection failure. The vehicle must be repaired and the code cleared.
• Texas: In counties requiring emissions testing, an active P1571 code with the Check Engine Light on causes the vehicle to fail the OBD-II portion of the inspection.

Most Commonly Affected Vehicles

• Chevrolet Corvette (1997-1998) — On all 1997 and some early 1998 models, P1571 is a 'phantom' code stored in history that cannot be cleared and does not indicate a real fault unless other symptoms or a current C1277 code are present. This is a known software sensitivity issue documented in GM TSB #PI00219.
• Ford Focus, Fiesta, Mondeo (2005-2018) — These models commonly report P1571 due to failures in the brake pedal position sensor or its wiring. The issue is widespread in this platform.
• GM (Chevrolet/GMC) Tahoe, Yukon, Silverado, Suburban (2000-2006) — This code often appears with P1689 and points to a communication problem between the PCM and the EBCM (ABS module), frequently caused by a faulty EBCM with internal cracked solder joints. Replacing a faulty EBCM with a used one from a vehicle without traction control also causes this code.
• Honda Civic Hybrid (2004-2011) — On these hybrid models, P1571 points to a fault within the IMA (Integrated Motor Assist) system, often related to the Motor Control Module (MCM) or its associated sensors, not the brake switch.
• Jaguar XF, XJ, XK (2007-2015) — On these models, P1571-64 is frequently caused by a software communication glitch between the PCM and the Park Brake Module, not a faulty switch. TSB SSM-71218 advises clearing codes first before replacing parts, especially if U0100 is also present.
• Kia / Hyundai Various (2007-2014) — For many Kia and Hyundai vehicles, P1571 corresponds to a 'Brake Switch Malfunction'. This was the subject of major recalls (NHTSA Campaign Numbers 13V114000 and 17V812000) for switches that fail, causing brake lights to not work or stay on.
• Subaru Legacy, Forester, Tribeca, Impreza (2005-2014) — On these vehicles, P1571 indicates an immobilizer problem, specifically a reference code mismatch between the immobilizer module and the engine computer (ECM), which prevents the engine from starting. This happens after battery replacement or if a key is not programmed correctly.
• Toyota RAV4, Camry (2006-2012) — For Toyota, P1571 indicates 'Lost Communications With Steering Angle Sensor'. This points to an issue in the communication line between the steering sensor and other control modules, not the brake system.
• Volkswagen / Audi A8, A6, Touareg (2004-2010) — On many VW and Audi models, P1571 is defined as 'Left Engine Mount Solenoid Valve - Short to B+'. This is unrelated to the brake system and points to a wiring or component fault in the active engine mount system.

Manufacturer-Specific Notes

• General Motors: P1571 refers to the 'Traction Control Torque Request Circuit'. This is a PWM signal the ABS module sends to the engine computer to request a reduction in engine power during wheel slip. GM issued recalls for EBCM software errors causing unintended braking.
• Chevrolet (Corvette): On all 1997 Corvettes, P1571 is stored in history and cannot be cleared. This is a known software glitch (TSB #PI00219) and must be ignored if there are no other symptoms or active codes.
• Jaguar: Per TSB #SSM-71218, code P1571-64 on the XF, XJ, and XK is a software communication issue between the PCM and Park Brake Module. Replacing the brake switch does not resolve this condition.
• Subaru: Relates to the anti-theft immobilizer system. The security reference code stored in the Engine Control Module (ECM) does not match the code in the immobilizer module, preventing the engine from starting.
• Kia / Hyundai: A faulty brake light switch is extremely common and caused massive recalls (NHTSA #13V114000 and #17V812000). Symptoms align directly with a failed switch: inoperative brake lights and inability to shift from Park.
• Volkswagen / Audi: Indicates 'Left Engine Mount Solenoid Valve Short to B+'. This system uses electronically controlled engine mounts to reduce vibration and has nothing to do with the brake system.

Real Owner Stories

2002 Chevrolet Tahoe with ABS/Brake lights on

Owner had ABS, Brake, and Traction Control lights on. They found code C0267 and tried to repair the EBCM by resoldering contacts, but it failed and burned the module. They installed a used EBCM from a junkyard.

Outcome: The used EBCM was incompatible. The fix required finding another used EBCM with the exact same part number and RPO code from a matching donor vehicle. After installation, the codes were cleared and did not return.

Lesson: For GM trucks, P1571 often points to the EBCM. When replacing with a used part, you must match the part number AND the RPO code (e.g., JL4 for Stabilitrak) exactly, or communication codes appear.

2013 Subaru BRZ with a no-crank, no-start condition

Bought a non-running BRZ. Diagnosed and had the dealer replace a bad SMT (Immobilizer) Module and reprogrammed it. The car still would not crank, and a scan tool showed code P1571 in the engine ECU.

Outcome: The final solution required the dealer to perform a full immobilizer and ECU synchronization procedure, ensuring the security codes matched across all related modules. Once the handshake was correctly established, the P1571 code cleared and the engine started.

Lesson: On a Subaru, P1571 is a critical immobilizer fault. Simply replacing one module is not enough; they must be electronically 'taught' to recognize each other by a dealer or specialist.

2009 Jaguar XF with 'Parking Brake Fault' and P1571

While driving, the 'Parking Brake Fault' message appeared, steering became heavy, and the engine died. The car would not crank. An RAC scan revealed P1571 and U0100 ('Lost communication with ECM/PCM').

Outcome: Instead of replacing the brake switch or park brake module, the owner first tried replacing the aging battery, as low voltage is a known trigger for these communication faults on Jaguars. A new battery and clearing the fault codes resolved the issue completely.

Lesson: On Jaguars, do not immediately replace the brake switch for P1571, especially if U0100 is present. Check for TSBs and test the battery first. A weak battery causes numerous communication codes.

How to Prevent This Code From Triggering

• Apply Dielectric Grease to Connectors (Whenever a relevant connector is disconnected) — Applying a thin layer of non-conductive dielectric grease to the connector seals keeps moisture and road salt out. This prevents pin corrosion, which causes high resistance and communication faults.
• Periodically Clean EBCM and Wheel Speed Sensors (Every 30,000 miles or annually) — Gently cleaning the module and its main connector of mud and debris prevents moisture buildup. Cleaning grime from wheel speed sensors ensures the ABS system gets accurate data.
• Ensure Battery Health and Clean Terminals (Every oil change) — A healthy, fully charged battery provides stable voltage. Low or fluctuating voltage causes modern control modules to glitch and post communication codes like P1571.
• Use a Memory Saver During Battery Replacement (Every battery change) — Plugging a memory saver device into the OBD-II port provides temporary power to the vehicle's modules while the main battery is disconnected. This prevents the loss of synchronization data.
• Fabricate a Heat Shield for the EBCM (Once) — For modules mounted near engine exhaust components, excessive heat is a primary cause of internal solder joint failure. Fabricating a simple aluminum heat shield deflects radiant heat.

Frequently Asked Questions

Can a bad battery cause a P1571 code?

Yes, a weak or failing battery causes insufficient or unstable voltage to various modules. This leads to communication errors and triggers a P1571 code indirectly, especially on sensitive European vehicles. Always ensure the battery reads 12.5V+ with the engine off and 13.5-14.5V with the engine running.

Why did P1571 appear after I replaced my battery or jump-started the car?

Disconnecting or replacing a battery causes modules to lose their learned settings or communication sync, particularly the immobilizer system on a Subaru. A voltage spike from a jump-start also triggers temporary communication glitches. Clearing the codes and driving the vehicle often allows the systems to re-synchronize.

What are the most common misdiagnosis mistakes for P1571?

The biggest mistake is immediately replacing the brake light switch without checking the manufacturer's specific definition. For example, P1571 is a phantom code on 1997 Corvettes, a software glitch on Jaguars (TSB SSM-71218), and an immobilizer issue on Subarus. Always check for Technical Service Bulletins (TSBs) before buying parts.

Will clearing the code fix the problem?

No, unless the code was triggered by a temporary glitch like a low battery. Clearing the code only erases the error message temporarily. The code returns as soon as the computer detects the underlying fault again.

How much does it cost to fix a P1571 code?

The cost depends entirely on the cause. A simple brake light switch replacement costs between $85 and $210 for parts and labor. A GM EBCM module mail-in repair service costs $300-$500, while a Subaru immobilizer reset at the dealer costs $100-$200.

Why won't my car start and I have a P1571 code?

If you have a Subaru, this code means an immobilizer issue is actively preventing the engine from starting. On other cars, if you cannot shift out of Park because of the faulty brake signal, you cannot start the car in any gear other than Park or Neutral.

Can I bypass the brake switch to start my car?

While technically possible to bypass the shift interlock solenoid, it is highly dangerous and not recommended. Doing so creates significant safety risks and damages the vehicle's electrical systems. The proper solution is to diagnose and repair the root cause.

Does P1571 affect remote start?

Yes, most factory and aftermarket remote start systems will not engage if there is an active Check Engine Light. The system sees a fault with a critical safety input like the brake switch and disables remote start as a safety precaution.

Key Takeaways

• P1571 is a manufacturer-specific code that indicates a $85 brake switch failure on Ford and Kia, a traction control fault on GM, or a critical immobilizer lockout on Subaru.
• Look for 3 immediate symptoms: an illuminated Check Engine Light, disabled cruise control, and brake lights that either stay on continuously or fail to illuminate.
• Search for Technical Service Bulletins (TSBs) before buying parts, as Jaguar TSB SSM-71218 and GM TSB PI00219 identify software glitches that trigger P1571 without any hardware failure.
• On Subaru models from 2005-2014, P1571 prevents the engine from starting and requires a dealer to re-synchronize the immobilizer and engine computer.
• On GM trucks from 2000-2006, P1571 frequently pairs with code P1689 to indicate a fractured solder joint inside the Electronic Brake Control Module (EBCM), requiring a $150-$400 mail-in repair.