C0040 on 2013-2019 Honda Civic: Brake Light Switch Failure Fix

What's Unique About the 2013-2019 Honda Civic

This is a classic case of a manufacturer-specific code causing confusion. Honda repurposed code C0040 to refer to a brake switch circuit issue. The problem is rarely the switch itself, but a tiny, brittle plastic stopper pad on the brake pedal arm that shatters with age. When this pad breaks, the switch plunger passes through the now-empty hole, making the car think the brakes are always applied. Ignoring this specific Honda definition leads many to mistakenly diagnose and replace the right front wheel speed sensor, which is the generic definition for C0040.

Generation note: This issue affects both the ninth generation (2013-2015) and tenth generation (2016-2019) Honda Civic. The cause, symptoms, and repair process involving the brake pedal stopper pad are identical for both generations. The same part number is used across a vast range of Honda and Acura models for decades.

Symptoms You May Notice

• Multiple warning lights on the dashboard, including ABS, VSA (traction control), and Power Steering.
• Brake lights are stuck on, even when the car is turned off.
🎬 Watch: Quick tip on Honda brake lights staying on
• Dead battery, caused by the brake lights staying on overnight.
• Cannot shift the transmission out of Park without using the manual override.
• Cruise control does not work.
• Finding small, broken pieces of blue, yellow, or white plastic on the driver's side floor mat.

Most Likely Causes

1. Disintegrated Brake Pedal Stopper Pad 🔴 High Probability → Shop Brake Pedal The plastic material used for the original stopper pad (part #46505-SA5-000) becomes brittle over time due to heat cycles and age, eventually shattering. This is a well-documented failure point across nearly all Honda and Acura models from the 1990s through the 2020s.
   How to confirm: Look at the brake pedal arm under the dashboard. You will see a small switch with a plunger. The pedal arm should have a small, solid plastic pad that presses this plunger when the pedal is released. If you see an empty hole where the plunger goes through, and/or plastic debris on the floor, the stopper has failed.
   Typical fix: Replace the stopper pad by snapping a new one into the hole on the brake pedal arm. 🎬 See this step-by-step brake pedal stopper replacement walkthrough It can be helpful to press the brake pedal down with your hand to get better access to the hole.
   Est. part cost: $5-$15

Rare But Worth Checking

• Faulty Brake Light Switch: → Shop Brake Light Switch While possible, this is far less common than the stopper pad failure. If the stopper pad is intact and properly depressing the switch plunger, but the symptoms persist, the switch itself may have failed internally. This would require testing the switch for continuity.
• Faulty Brake Light Relay: In some Honda models, a stuck brake light relay can cause the lights to stay on. If the stopper pad and switch are confirmed to be good, the relay in the under-hood fuse box could be the culprit.
• VSA/ABS Modulator Fault: In very rare cases, after all other possibilities are exhausted, the VSA/ABS control unit could be the source of the problem. This is an expensive and unlikely cause.

Diagnosis Steps

1. Check the driver's side floor mat for small, broken pieces of colored plastic.
2. With the car off, observe the rear of the vehicle to see if the brake lights are illuminated.
3. Look under the driver's side dashboard at the top of the brake pedal arm.
4. Identify the brake light switch, which has a small white or black plunger that points towards the pedal arm.
5. Observe the point on the pedal arm that contacts the switch plunger. If there is an empty hole instead of a solid surface, the stopper pad has failed.
6. If the stopper pad is intact, have an assistant watch the brake lights while you manually depress and release the switch plunger to see if the switch is functioning correctly.
7. If the stopper pad is intact and the switch tests good, consider checking the brake light relay.
8. If all other components test good, further diagnosis of the VSA/ABS module by a professional may be needed.

Parts You'll Likely Need

• Brake Pedal Stopper Pad (OEM #46505-SA5-000) — This is the component that fails 99% of the time for this code on this vehicle. It is designed to press the brake light switch plunger, and it disintegrates with age.
  Trusted brands: Genuine Honda, Dorman (HELP! line, part #74015)
  OEM price range: $5-$10
  Aftermarket price range: $5-$15

Platform-Specific Known Issues

• As a temporary fix while waiting for the part, some owners have used a small bolt and nut, or even stacked coins taped into the hole to depress the switch plunger. This is not recommended for long-term use as an improper object can damage the switch or fall out, but it can prevent the battery from draining. One owner reported overheating their brakes after an improperly sized bolt caused slight, constant brake application on the highway.

Mechanic-Grade Diagnostic Values

• Brake Light Switch Continuity (Brake Light Circuit) — expected: With the switch plunger extended (simulating brake pedal pressed), there should be continuity (near 0 Ω resistance). With the plunger depressed (pedal released), the circuit should be open (infinite resistance).. Failure: Continuity when the plunger is depressed, or an open circuit when the plunger is extended, indicates a faulty switch.
• Brake Light Switch Continuity (Cruise Control/ECU Circuit) — expected: Many Honda switches have a second, separate circuit for the cruise control and ECU that works in the opposite way. With the plunger extended (pedal pressed), the circuit is open. With the plunger depressed (pedal released), there is continuity.. Failure: If this circuit fails, it can prevent cruise control from working but may not trigger the C0040 code, which is specific to the brake lights being stuck on.

Hidden / Shadow Codes Worth Checking

• C0040-62: This is the full Honda-specific DTC, which translates to 'Brake Lamp Switch Failure (Stuck)'. The '-62' suffix provides the specific failure mode information that is often not visible on generic OBD-II scanners. (see via A professional-grade scanner or the Honda Diagnostic System (HDS) is required to view the full sub-code.)

Scan Tool Commands That Help

• Honda Diagnostic System (HDS): VSA System DTC Check / Clear — Used to retrieve and clear specific VSA system codes like C0040-62 after a repair has been completed.
• Honda Diagnostic System (HDS): VSA Modulator-Control Unit Update — In rare cases, a software glitch can cause VSA issues. HDS can check if the VSA module has the latest software and update it if necessary. This is typically performed after replacing the VSA modulator itself.
• Honda Diagnostic System (HDS) or advanced scanner: VSA Sensor Neutral Position Memorization — This calibration procedure is required after replacing the VSA modulator-control unit or yaw rate-lateral acceleration sensor to ensure the system has a correct baseline. It may also be required after clearing certain complex VSA faults.

Wiring & Ground Locations

• Brake Light Switch Connector — Directly on the brake light switch, located at the top of the brake pedal arm under the driver's side dashboard.. This 4-pin connector provides power to the switch and sends the signal to the brake lights and various control modules. A poor connection here could mimic a switch failure.
• Ground Point G401 — On some Honda models, this is a common ground point located far up behind the left side of the dashboard, near the driver's kick panel area.. A loose or corroded ground connection for the brake light circuit could potentially cause erratic behavior, although it is a much rarer cause than the stopper pad failure.

Real Owner Repair Stories

• YouTube channel 'Global Commerce CA' (2016 Honda Accord V6) — Multiple warning lights on the dash including skid control, lane assist (LKAS), and power steering. Scan revealed code C0040 for brake switch stuck on.
  ❌ Tried (didn't work) Unplugging the brake light switch connector did not turn the brake lights off, indicating the problem was further down the circuit.
  ✅ What actually fixed it The brake light relay, located in the under-hood fuse box, had failed internally. The contacts were permanently bridged, causing the brake lights to stay on regardless of the switch's position. Replacing the relay resolved the issue.
• Reddit user on r/MechanicAdvice (Honda Civic (year not specified, but behavior is identical)) — Dead battery from brake lights staying on overnight. Found broken plastic stopper pieces on the floor mat.
  ❌ Tried (didn't work) A temporary fix using a 10mm bolt that was too small. It worked for a few days in the city.
  ✅ What actually fixed it The issue was the broken stopper pad. However, the temporary bolt fix led to a secondary, severe problem: on the highway, the bolt caused the brakes to drag constantly, leading to extreme overheating of the entire brake system (pads, rotors, calipers, fluid), smoking, and a spongy pedal feel requiring replacement of multiple brake components. This story serves as a cautionary tale against improper temporary fixes.

OEM Part Supersession History

• 46505-SA5-000 → This part number remains the primary active number, but it also replaces several older, discontinued numbers. — Part consolidation over decades of use.
  Heads up: Replaces older part numbers 46505-SA5-010, 46505-579-000, 46505-SH3-000, and 46505-659-000. All are interchangeable for this application.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Oil Dilution (1.5L Turbo Engine) 🔴 High — Common on 2016-2018 models, especially in cold climates with frequent short trips. Can occur at low mileage (<30,000 mi). (Ref: Honda issued software updates and extended warranties (e.g., TSB 18-137) to address the issue.)
• A/C System Failures (Condenser/Compressor) 🟠 Medium — Widespread on 10th gen (2016-2019) Civics. Condensers are prone to leaks and compressors can fail. Honda extended the warranty on condensers for many models. (Ref: Warranty extensions issued for A/C condensers on certain models.)
• Sticky Steering (10th/11th Gen) 🔴 High — Affects some 10th gen (2016-2019) and is more prominent on 11th gen (2022+) Civics, often at low mileage. Causes momentary increased steering effort at highway speeds. (Ref: TSB 23-037 instructs dealers to replace the electronic power steering gearbox.)
• Bad Engine Mounts (9th Gen) 🟠 Medium — Common on 9th gen (2012-2015) models, causing vibrations at idle, roughness, and clunking noises when shifting.
• Carbon Buildup on Intake Valves (1.5L Turbo Engine) 🟠 Medium — A long-term issue inherent to direct-injection engines like the 1.5T. Typically requires cleaning every 50,000-70,000 miles to prevent misfires and performance loss.
• Harsh Shifting (9th Gen Automatic/CVT) 🟡 Low — Some 9th gen (2012-2015) owners report harsh 1-2 shifts in the 5-speed automatic, potentially related to a shift solenoid. The 2014-2015 CVT had a recall for a software update to prevent pulley damage. (Ref: Recall for 2014-2015 CVT software.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, buying a used part is strongly discouraged. The primary failure part, the plastic stopper pad, fails due to age and heat-induced brittleness; a used one would be just as likely to fail. A used brake light switch or relay could be considered in a pinch, but their low cost new makes it an impractical choice.

What to inspect on the donor part:

• Not applicable, as new parts are inexpensive and recommended.

OEM-only on this vehicle (don't cheap out):

• Brake Pedal Stopper Pad (46505-SA5-000): While aftermarket versions exist (like Dorman 74015), the Genuine Honda part is extremely inexpensive and is guaranteed to fit and be made of the most current material specification. Given the low cost, there is little reason to use an alternative.

Brands owners have reported issues with on this vehicle:

• Unknown/no-name brands for the brake light switch or relay. Stick to Genuine Honda or a reputable OEM supplier if not buying from the dealer.

Documented NHTSA Reports

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• TSB 18-137 — While not a diagnostic code, this TSB relates to the 1.5L Turbo engine oil dilution issue common in 2016-2018 Civics, which can occur alongside other electronic warnings.
• TSB 23-037 — Related to electronic power steering gearbox replacement for the 'sticky steering' issue found in 2016-2019 models.

Frequently Asked Questions