CODE MEANING AND SEVERITY
- What the code means: P0571 is a Cruise Control/Brake Switch A Circuit fault. In the Subaru Forester, this code indicates the brake switch signal that tells the engine computer (ECU) or cruise control system that the brake pedal is pressed is not reading correctly, or the circuit is out of range. The “A Circuit” designation generally refers to the primary brake switch input used by cruise control (and sometimes the second switch or related wiring). When the ECU detects an abnormal signal on this input, it stores P0571.
- How severe it is: Moderate. It typically disables or prevents the cruise control from engaging and may cause intermittent cruise-control behavior or a lit MIL (check engine light). It is not a direct engine or safety-critical fault, but because it affects cruise control and can indicate a brake switch/wiring problem, it should be diagnosed and repaired to restore proper cruise control function and ensure brake switch reliability.
COMMON CAUSES ON SUBARU FORESTER
- Faulty brake light/Brake Switch (A circuit) or misadjusted brake pedal switch: The most common cause. If the switch is out of alignment, failing, or not producing a clean signal, the ECU may see an abnormal brake-switch input.
- Damaged or corroded wiring or connectors to the brake switch or cruise control input: Wires can be pinched, chafed, or corroded at connectors (especially in humid regions or where the harness sits near movement/brake components).
- Faulty cruise control system module or related ECU input: A failing module or a fault in the signal path from the brake switch to the cruise control logic can trigger P0571.
- Intermittent ground or power supply issues on the brake switch circuit: A loose ground or intermittent power can create erratic readings.
- Aftermarket accessories or modifications affecting brake switch wiring: Modifications near the pedal area or harness routing can cause interference or poor signal.
- Less common: Brake-light-related issues that indirectly affect the circuit (e.g., a brake-light switch that affects multiple circuits or a short to ground in the switch harness).
SYMPTOMS
- Cruise control will not engage or will disengage when attempting to hold speed.
- Cruise control indicator on the dash may not illuminate or may behave erratically.
- Brake lights function correctly or may stay on intermittently if the switch is faulty, leading to a noticeable brake-light issue.
- Intermittent or persistent MIL (check engine light) with P0571 stored.
- Occasional misinterpretation of brake pedal position by the cruise-control logic, causing unexpected disengagements.
- In rare cases, other related codes (P0570, P0572, P0573, P0574) may appear if the circuit has multiple issues.
DIAGNOSTIC STEPS
Note: Start with quick, non-invasive checks before opening harnesses. Document any related codes and freeze-frame data.
Verify the code and collect data
- Use an OBD-II scan tool to confirm P0571 is present and check for any related codes (e.g., P0570, P0572, P0573, P0574).
- Review freeze-frame data for brake pedal activity, cruise-control status, and vehicle speed when the fault occurs.
Inspect the brake lights and switch
- Confirm brake lights illuminate normally when the pedal is pressed and turn off when released.
- Visually inspect the brake light switch at the brake pedal for visible damage, misalignment, or looseness.
- Check the brake pedal travel and switch adjustment: if the switch appears out of position, adjust per service manual.
Test the brake switch signal
- With the ignition on (engine off or in park as appropriate for Subaru procedures), test the brake switch signal with a multimeter:
- Identify the brake light switch connector(s) (A and possibly B circuits). One circuit feeds the brake lights; the other provides the signal to the cruise control ECU.
- When you depress the brake pedal, the switch should change state (continuity or voltage change) in a predictable way. When not depressed, it should be the opposite.
- Confirm continuity/voltage changes are clean and repeatable across pedal travel. Look for intermittent behavior or a signal that does not switch properly.
Inspect wiring and connectors
- Check wiring harness from the brake switch to the ECU/cruise control input for cuts, chafing, or pin damage.
- Inspect connectors for corrosion, bent pins, or loose fits. Reseat and clean as needed.
- Look for signs of heat damage, moisture intrusion, or rodent damage near the pedal area.
Check fuses and power/ground integrity
- Locate the fuse for the cruise control and related brake-switch circuits and verify it is intact.
- Check for proper power supply and ground on the brake-switch circuit when the pedal is pressed and released.
Test with live data and/or a scan tool
- If possible, monitor the Brake Switch A circuit input to the ECU while pressing and releasing the brake pedal. Confirm the signal is stable and within expected voltage or logic levels when the pedal is pressed vs. released.
- If the signal looks healthy, the fault could be intermittent wiring or the cruise-control module itself.
Rule out other related components
- If brake lights are functioning normally and the brake switch signal appears correct, consider testing or programming the cruise control module or ECU (some Forester models may require software updates, programming, or replacement if the module is faulty).
- If other related codes are present, follow their diagnostic paths as they may point to a broader control module or wiring issue.
Clear codes and retest
- After performing repairs, clear the codes and take a test drive to confirm P0571 does not return. Reproduce the fault conditions (brake apply, attempt to engage cruise control) to validate repair.
When to escalate
- If you cannot verify a clean brake-switch signal and wiring, or if the fault persists after brake-switch/wiring replacement, the issue may lie with the cruise-control module or the ECU. This typically requires professional diagnosis and possible module replacement or reprogramming.
RELATED CODES
- P0570 Cruise Control System Malfunction
- P0572 Cruise Control/Brake Switch B Circuit
- P0573 Cruise Control/Brake Switch A Circuit Range/Performance
- P0574 Cruise Control/Brake Switch B Circuit Range/Performance
REPAIR OPTIONS AND COSTS (2025 PRICES)
Notes:
Prices vary by region, shop, and whether parts are new, used, or remanufactured. All figures are approximate ranges as of 2025.
Labor times are typical estimates and may differ based on exact trim, access, and regional labor rates.
Brake Light Switch replacement (most common cause)
- Parts: $15–$60
- Labor: 0.5–1.0 hours
- Estimated total: $60–$180
Brake Pedal Position Switch replacement (if separate from the brake light switch)
- Parts: $30–$70
- Labor: 0.5–1.0 hours
- Estimated total: $100–$230
Wiring harness/connector repair or replacement (to fix damaged wiring or connectors)
- Parts: $0–$30 (if reusing existing harness) or up to $100+ for harness replacement
- Labor: 0.5–1.5 hours
- Estimated total: $80–$250
Cruise Control module or ECU-related repair (less common)
- Parts: $250–$700 (cruise control module or related ECU component)
- Labor: 1.0–2.5 hours
- Estimated total: $350–$1,000
Fuse/relay replacement or circuit repair
- Parts: $5–$20
- Labor: 0.1–0.5 hours
- Estimated total: $20–$100
Full system diagnostic by a shop
- Parts: N/A
- Labor: 0.5–2.0 hours
- Estimated total: $60–$200 (can vary by shop)
Misc. potential costs (if the condition leads to additional component issues)
- Brake switch misalignment causing brake-light issues can require panel removal or access work; costs will reflect labor time.
DIY vs PROFESSIONAL
DIY feasibility: Moderate. If you are comfortable with automotive electrical diagnostics, you can tackle the brake light switch/wiring inspection and basic testing.
- Pros: Lower cost, direct control, good learning experience.
- Cons: Risk of incorrect reassembly, misadjustment of switch, or missing more subtle wiring issues; some Subaru models require specific alignment procedures and reprogramming.
DIY steps you can handle:
- Inspect and adjust the brake light switch alignment at the brake pedal.
- Verify brake lights operate correctly with pedal press.
- Inspect connectors and wiring for obvious damage or corrosion.
- Use a multimeter to test continuity/voltage on Brake Switch A circuit when pedal is pressed vs released.
- Clear codes and test drive to verify behavior after basic fixes.
When to go to a professional:
- If the brake switch and wiring appear fine but P0571 persists.
- If you suspect a faulty cruise control module, ECU, or software issue.
- If there are intermittent signals, moisture intrusion, or you’re uncomfortable with electrical diagnosis.
- If your vehicle is under warranty or you want an official software update or re-flash.
PREVENTION
- Keep the brake switch properly aligned and intact; avoid rigid routing that rubs on pedals or metal edges.
- Inspect the brake switch and its connectors during routine service (or if you notice brake lights behaving oddly).
- Protect wiring harnesses from moisture, corrosion, and physical wear; ensure harness clips and grommets are in good condition.
- Use quality connectors and avoid aftermarket modifications that can interfere with brake-switch signals.
- Regularly test cruise control function to catch faults early.
- If your Forester is subject to software updates or recalls, verify you have up-to-date software and that any vehicle updates are performed by a Subaru dealer or qualified shop (note: the provided data shows no recalls in the current dataset).
DATA LIMITATIONS AND DISCLOSURES
- Real-world data provided: No owner complaints found and No recalls found in the NHTSA database for the 2019-2024 Subaru Forester relating to this issue.
- This guide uses general automotive knowledge and standard diagnostic practices for P0571. Absence of complaints or recalls in the provided data does not guarantee that issues cannot occur in specific vehicles or regions.
- Always verify current service information and prices for your exact vehicle variant, region, and dealership/service center.