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P1571 on 2009-2014 Hyundai Sonata: Brake Switch Circuit Malfunction Causes and Fixes

On a 2009-2014 Sonata, code P1571 is almost always caused by a disintegrated plastic brake pedal stopper pad (Part No. 32876-3Q100), a tiny part that costs under $10. This prevents the brake light switch from working correctly, causing symptoms like brake lights staying on, inability to shift from park, or a no-start condition. The fix is a very easy 15-minute DIY replacement. The second most common cause is a faulty brake light switch (Part No. 93810-3S000), also covered by a recall.

21 minutes to read 2009-2014 Hyundai Sonata

Most Likely Cause

Deteriorated Brake Pedal Stopper Pad

Difficulty

1/5

Est. Time

0.3 hrs

DIY Doable?

✅ Yes

Shop Labor

$50 – $120

Parts Price

$2 – $50

🚫 Do not drive — Continued driving is not recommended. Your brake lights may either be stuck on, confusing other drivers, or not work at all, which is a major safety hazard. You also risk being unable to start the car or shift it out of Park, potentially leaving you stranded.

Key Takeaways

P1571 on a 2009-2014 Sonata is almost certainly a brake signal issue, not a major computer or transmission problem.
Before buying any parts, check the driver's side floor for broken plastic bits and look at the brake pedal arm for a missing stopper pad. This is the most common cause and a sub-$10 fix.
This is a high-safety-impact issue. Do not drive the vehicle until fixed, as your brake lights may be malfunctioning.
Check if your vehicle has an open recall for either the stopper pad (Recall 136) or the switch (Recall 110), as the repair may be performed by a dealer for free.
The repair for either the stopper pad or the switch is very simple and can be done by a DIYer with basic tools in under 30 minutes.

P1571 is a manufacturer-specific code for Hyundai that means 'Brake Switch Circuit Malfunction'. The Engine Control Module (ECM) has detected an illogical or inconsistent signal from the brake light switch. This switch, located on the brake pedal arm, tells the car's computers when the brakes are applied. This signal is critical for operating the brake lights, cruise control, push-button start, and the automatic transmission shift interlock.

What's Unique About the 2009-2014 Hyundai Sonata

The 2009-2014 (YF generation) Sonata is highly susceptible to this code due to two widespread, documented issues. The most common is the failure of a small, brittle plastic 'stopper pad' on the brake pedal arm, which was the subject of a major recall (Hyundai Recall 136). This tiny part crumbles, letting the switch plunger pass through a hole, making the car think the brake is always pressed. A second, also common issue covered by another recall (Hyundai Recall 110), is the premature failure of the electronic brake light switch itself.

Generation note: The 2009-2014 range primarily covers the sixth generation (YF) Sonata, which launched for the 2011 model year in the US. Recalls for the most common causes specifically target the 2011-2012 models for the stopper pad and 2009-2011 for the switch, but the parts and issues are relevant to the entire generation and platform mates like the Kia Optima.

Symptoms You May Notice

Brake lights stay on even when the pedal is released
Brake lights do not turn on when the pedal is pressed
ESC (Electronic Stability Control) or Traction Control warning light is on
Unable to shift the transmission out of Park
Car with push-button start will not start
Cruise control cannot be set or deactivates unexpectedly
Intermittent operation of push-button start

⚠️ Don't Waste Money on the Wrong Fix

Replacing the battery when a push-button start model won't start. The no-start is often due to the computer not receiving the 'brake applied' signal, not a dead battery.
Assuming a faulty transmission shift interlock solenoid when the shifter is stuck in Park. The solenoid is usually functional but is not receiving the release signal from the brake switch.

Most Likely Causes

Deteriorated Brake Pedal Stopper Pad 🔴 High Probability → Shop Brake Pedal The original stopper pad material becomes brittle and crumbles over time due to material composition. This was the subject of Hyundai Recall 136 (NHTSA 15V759000) for 2011-2012 models, affecting over 300,000 vehicles.
How to confirm: Look on the driver's side floor mat for small, broken pieces of colored plastic. Then, look up at the brake pedal arm and you will see an empty hole where the brake light switch plunger goes through, instead of pressing against a pad. A YouTube video by 'Fixing it Forward' titled 'Hyundai Sonata brake light staying on and lack of acceleration easy fix' clearly shows the disintegrated part and replacement.
Typical fix: Replace the stopper pad. It is a small plastic grommet that simply pushes into the hole on the brake pedal arm. This is a well-documented DIY fix that takes less than 15 minutes. 🎬 Watch: Quick DIY fix for stuck-on brake lights
Est. part cost: $2-$10
Faulty Brake Light Switch 🟡 Medium Probability → Shop Brake Light Switch The switch itself is prone to internal failure, causing intermittent contact. This was the subject of Hyundai Recall 110 (NHTSA 13V113000), which covered over 1.7 million Hyundai vehicles, including the 2009-2011 Sonata.
How to confirm: If the stopper pad is intact, the switch is the next likely culprit. A multimeter can be used to test for continuity across the switch's 4 pins when the plunger is depressed and released. A malfunctioning switch may cause brake lights not to work at all, whereas a failed stopper pad usually causes them to stay on.
Typical fix: Replace the brake light switch. This involves unplugging the electrical connector, unscrewing the old switch from its bracket, and installing the new one, ensuring proper adjustment. 🎬 Watch: Step-by-step brake light switch replacement demo
Est. part cost: $15-$50
Blown Fuse ⚪ Low Probability
How to confirm: Check the vehicle's fuse boxes (both in the cabin and engine bay) for any blown fuses related to the brake lights ('STOP LP'), stop lamps, or ECU. The main fuse to check is the 15A 'Stop Lamp' fuse in the driver's side interior fuse panel.
Typical fix: Replace the blown fuse with a new one of the same amperage.
Est. part cost: $1-$5

Rare But Worth Checking

Wiring Harness Issue: A forum user reported that a wiring harness was improperly routed from the factory, causing a wire to chafe against a moving part and short out, leading to repeated brake switch failure.
Low Battery Voltage: A weak or failing battery can cause numerous, seemingly unrelated electronic glitches and communication codes, including brake switch errors.
Misadjusted Brake Light Switch: → Shop Brake Light Switch Even a functional switch can cause these symptoms if it is not installed and adjusted correctly. If the plunger is not depressed enough when the pedal is at rest, the car will think the brakes are always on. If it's too far, the lights may not activate when the pedal is pressed. Proper adjustment is critical after replacement.

Diagnosis Steps

Check for Recalls: First, use your VIN to check the NHTSA or Hyundai website for open recalls related to the brake pedal stopper pad (Recall 136 / NHTSA 15V759000) or the brake light switch (Recall 110 / NHTSA 13V113000).
Inspect the Floor: Look on the driver's side floor mat for broken plastic fragments. This is the tell-tale sign of a failed stopper pad.
Inspect the Brake Pedal Arm: Look above the brake pedal to where the brake light switch makes contact. If you see a small hole and the switch's plunger goes right through it, the stopper pad is missing and is the cause of your problem.
Test Brake Lights: Have a helper observe the brake lights. Are they stuck on? This usually points to a failed stopper pad. Do they not light up at all? This often points to a failed switch or blown fuse.
Check Fuses: If the stopper pad is intact and lights don't work at all, check the 'STOP LP' fuse in the interior fuse panel.
Test the Switch: If the stopper pad is good and the fuse is okay, the switch itself is the likely suspect. It can be tested with a multimeter for proper operation. The TSB for recall 110 provides a procedure for testing the switch by checking if the brake lights turn on/off when the plunger is released/depressed.

Parts You'll Likely Need

Brake Pedal Stopper Pad (OEM #32876-3Q100) — This is the most frequent failure point. The original part deteriorates, crumbles, and falls out, causing the P1571 code. The updated part is made of a more durable material.
Trusted brands: Genuine Hyundai
OEM price range: $5-$10
Aftermarket price range: $2-$8
Brake Light Switch / Stop Lamp Switch (OEM #93810-3S000) — The second most common cause, this 4-pin electronic switch fails internally, leading to intermittent or total loss of the brake signal. This was the subject of a large-scale recall.
Trusted brands: Genuine Hyundai, Beck/Arnley, Standard Motor Products
OEM price range: $25-$50
Aftermarket price range: $15-$35

Related Codes That Often Appear With This One

C1513 — This is a more specific 'Brake Switch Error' code. A Hyundai TSB notes this code can be triggered when the stopper pad is missing, as the switch remains on for an extended period (over 60 seconds) without brake pressure being applied.
P0504 — This is a generic OBD-II code for 'Brake Switch A/B Correlation'. The 4-pin switch has two separate internal switches. This code sets when the ECM sees an illogical combination of signals from those two switches (e.g., one says the pedal is pressed while the other says it's released).

Technical Service Bulletins (TSBs) & Recalls

TSB 16-01-007: This TSB supersedes a previous version and provides the service procedure for replacing the brake pedal stopper pad under Recall 136. It explicitly adds a step to check and set the stop lamp switch gap to 1.0-2.0mm after replacement.
TSB 15-01-056: The original TSB for Recall 136, detailing the replacement of the stopper pad.
TSB for Recall 110: Details the replacement procedure for the faulty stop lamp switch. It notes to ensure the new part is the updated version and not the original one marked 'INFAC'.

Platform-Specific Known Issues

Hyundai Recall 136 (NHTSA 15V759000): Addresses the deteriorating brake pedal stopper pad on 2011-2012 Sonatas. The fix is to replace the pad with an improved part (32876-3Q100).
Hyundai Recall 110 (NHTSA 13V113000): Addresses the failing brake light switch on 2009-2011 Sonatas (and many other Hyundai models). The fix is to replace the switch.

Mechanic-Grade Diagnostic Values

Brake Light Switch Continuity Test (4-Pin Switch) — expected: With the switch removed: Pins 1 & 2 should have continuity when the plunger is released (pedal pressed) and no continuity when the plunger is depressed (pedal released). Pins 3 & 4 work the opposite way: no continuity when the plunger is released, and continuity when the plunger is depressed.. Failure: If either pair of pins does not switch between continuity and open circuit as the plunger is operated, the switch is faulty.
Brake Light Switch Input Voltage — expected: With the ignition on, one of the four pins at the connector should show battery voltage (~12V) at all times. This is the power feed from the fuse.. Failure: No voltage on any pin indicates a problem upstream, likely a blown 'STOP LP' fuse or a wiring issue.
Brake Light Switch Output Voltage — expected: When the brake pedal is pressed, the output pin for the brake lights should show battery voltage (~12V).. Failure: If input voltage is present but output voltage does not appear when the pedal is pressed, the switch is faulty.
Stop Lamp Switch Gap — expected: 1.0 - 2.0mm. This is the specified clearance to check after installing a new stopper pad, according to Hyundai TSB 16-01-007.. Failure: Incorrect gap can lead to the switch not activating or deactivating properly, mimicking a failed part.

Scan Tool Commands That Help

Hyundai GDS (Global Diagnostic System): Current Data / Data Analysis — The GDS can monitor the live status of the brake switch ('Select Lever Switch') as seen by the car's modules. This is useful for diagnosing intermittent issues or confirming if a misadjusted switch is sending a constant 'on' or 'off' signal.
Hyundai GDS (Global Diagnostic System): Flight Recorder — For intermittent faults where the symptoms don't appear on demand, the GDS flight recorder can be activated. It continuously buffers data and saves a recording of the time period *before* the technician hits the trigger, helping to capture the data from an elusive event.

Wiring & Ground Locations

Stop Lamp Switch Connector — Located directly above the brake pedal arm, under the driver's side dashboard.. This 4-pin connector is the primary interface for the switch. Testing for power, ground, and signal output happens here. Corrosion or loose pins can mimic a failed switch.
Interior Fuse Box ('Stop Lamp' fuse) — On the driver's side of the dashboard, typically behind a small removable panel near the driver's left knee.. This is the location of the 15A fuse that protects the brake light circuit. It is a primary check if the brake lights do not work at all.
Ground Point (e.g., MM01) — Various ground points are located throughout the cabin, often bolted to the chassis behind kick panels or under the dash. For the 2014 Sonata, ground point MM01 is a key grounding location in the driver-side dash area.. A poor ground connection for the brake light circuit can cause intermittent or no operation. While not a common cause for this specific code, it's a possibility in cases of unusual electrical issues.

Real Owner Repair Stories

YouTube user PSK AUTO (Hyundai (model not specified, but demonstrates the common 4-pin switch)) — Brake lights would not shut off after installing a new switch.
❌ Tried (didn't work) The new switch was installed, but the problem persisted.
✅ What actually fixed it The new brake light switch was misadjusted. The threaded body of the switch allows for adjustment to set the correct distance between the plunger and the pedal arm. By carefully adjusting the switch in and out, a 'sweet spot' was found where the lights operated correctly.
YouTube user boris donovan (2011 Hyundai Sonata) — Push-button start would not work, displaying 'press brake pedal to start engine' message even with the pedal depressed.
❌ Tried (didn't work) Initially suspected a faulty brake light switch.
✅ What actually fixed it The 15A 'Stop Lamp' fuse in the interior fuse box was blown. Replacing the fuse resolved the no-start condition.

OEM Part Supersession History

93810-3K000 → 93810-3S000 (or 93810-3K000QQH) — The original switch was prone to failure and was the subject of a major recall (Recall 110). The new part is an updated design for improved reliability. The color of the connector body was changed from black to gray on the new part.
Heads up: Never install the old version of the switch (often marked 'INFAC') into a vehicle covered by the recall. While it may fit, it is known to be faulty.

Model Year Variations Within This Range

2009-2011: These model years were the primary focus of Recall 110 for the faulty brake light switch itself.
2011-2012: These model years were the primary focus of Recall 136 for the deteriorating brake pedal stopper pad.

Diagnostic Flowchart

P1571 on this platform typically points to a Brake Switch Signal Malfunction. Start by checking for physical debris on the floorboard and verifying brake light operation.

Inspect the driver's side floor mat. Do you see small fragments of colored plastic or a hole in the brake pedal arm where the switch plunger meets it?

→ Replace the Brake Pedal Stopper Pad (Part 32876-3Q100). This is a common failure addressed in Hyundai Recall 136 (NHTSA 15V759000) for 2011-2012 models. Ensure the switch gap is set to 1.0-2.0mm per TSB 16-01-007.

Using a multimeter, test for continuity across the 4-pin brake light switch. Does the switch fail to toggle signal when the plunger is depressed?

→ Replace the Brake Light Switch. This was the subject of Hyundai Recall 110 (NHTSA 13V113000). Ensure the replacement part is the updated version and not the original 'INFAC' branded unit.

Does the vehicle have a push-button start, and is it experiencing intermittent starting or inability to shift out of Park?

→ Even if the switch tests okay for lights, the secondary circuit for the Smart Key unit may be failing. Replace the switch as a preventative measure per Recall 110 guidelines for 2009-2011 models.

→ Inspect the wiring harness connector at the brake switch for loose pins or corrosion. If the P1571 persists, check the ABS/ESC module for communication errors.

Have an assistant watch the rear of the car. Do the brake lights turn on when the pedal is pressed?

Check the 15A 'STOP LP' fuse in the driver's side interior fuse panel. Is the fuse blown?

→ Replace the 15A fuse. If it blows again immediately, inspect the wiring harness for a short circuit, common in high-mileage YF platform vehicles.