The message indicates your center high-mounted stop lamp (CHMSL) isn’t functioning properly and needs attention. The CHMSL is the brake light mounted high on the rear of the vehicle to improve visibility for drivers behind you. A warning can be triggered by a burnt-out bulb or LED, a blown fuse, worn wiring, or a fault in the body control module that monitors the brake-light circuit.
What is the high-mounted brake light (CHMSL)?
The following points describe the CHMSL and why it matters.
- Location: typically mounted high on the rear of the vehicle, often at the top of the rear window or hatch.
- Purpose: improves visibility to drivers behind you during braking, especially in heavy traffic or poor light.
- Regulatory role: safety standards in many regions require a CHMSL on new vehicles to reduce rear-end collisions.
- Technology: can be traditional bulbs or modern LEDs; some vehicles use a dedicated CHMSL module separate from other brake lights.
In short, the CHMSL is a safety feature designed to enhance braking visibility. If it isn’t working, you should inspect and fix it to maintain safety and compliance.
What does the warning mean?
The warning can indicate several possible faults in the CHMSL system or its common circuits. Common causes include the following:
- Burnt-out or failed CHMSL bulb or LED segment (or a loose connection in the light assembly).
- Blown fuse or a fault in the brake-light circuit fuse.
- C damaged or corroded wiring, moisture intrusion, or a faulty connector at the CHMSL housing.
- Faulty body control module (BCM) or brake-light control circuit that monitors the CHMSL.
- A separate issue with the brake light switch or related wiring that affects rear brake-light operation.
Because the CHMSL is a safety-critical signal, a warning should be treated promptly. Even if only one lamp appears dim or intermittent, address it before driving extensively.
How to diagnose and fix a CHMSL warning
Use a step-by-step approach to identify and correct the issue.
- Turn on the brake pedal and have an assistant check all rear brake lights, including the CHMSL, to see if any lamp is out or dim.
- Visually inspect the CHMSL for signs of a burnt-out bulb, broken lens, moisture, or corrosion in the housing.
- Check the relevant fuse(s) for the brake-light circuit and replace any blown fuse with the correct rating.
- Inspect the wiring and connectors at the CHMSL for damage, loose connections, or moisture; reseat connectors and clean corrosion if needed.
- If the CHMSL uses LEDs, consider replacing the entire CHMSL unit if individual LEDs are not serviceable or the module shows an internal fault.
- If the lamp and wiring appear intact, use an OBD-II scanner or consult the vehicle’s service manual to check for fault codes related to the brake-light circuit or BCM; follow manufacturer guidance to repair or replace components.
Once the issue is addressed, re-check all rear brake lights to confirm the CHMSL is functioning properly. If the warning persists after basic checks, seek professional service to diagnose potential BCM or wiring faults.
Regulatory context and maintenance tips
Understanding the regulatory backdrop and adopting simple maintenance can prevent future issues.
- Regulatory context: Safety standards in many regions (including FMVSS 108 in the United States and corresponding EU regulations) require reliable CHMSL operation on new vehicles to reduce rear-end collisions.
- Preventive maintenance: Regularly inspect the CHMSL and other rear brake lights, replace failing lamps promptly, and check fuses and wiring as part of routine vehicle maintenance.
- Part considerations: LED CHMSL assemblies are common on newer vehicles; they may be more durable but can be more costly to replace than traditional bulbs.
Maintaining a functional CHMSL supports road safety and helps ensure compliance with applicable regulations and vehicle inspections.
Summary
A “Check High Mounted Brake Light” warning signals a fault in your center high-mounted stop lamp. Start with a visual check of the CHMSL bulb or LED, inspect fuses and wiring, and verify the brake-light circuit. If basic checks don’t resolve the issue, replace the CHMSL module or consult a qualified technician to diagnose potential BCM or wiring faults. Keeping the CHMSL in good condition improves braking visibility for drivers behind you and helps meet safety standards.
How much to replace a high-mounted brake light?
The cost of aftermarket third brake light bulbs may range between $50 and $250 for parts alone. Several factors affect pricing, such as brand, warranty, color or finish, light source, and set inclusions. Labor may cost you an additional $25 to $75 depending on the rates in your area.
Can I drive with a check brake wear light on?
It's always alarming when a warning light suddenly appears on your dashboard, but it's important not to panic if it happens. In many cases, you can continue driving as long as you get the issue checked out quickly. Other situations may require you to safely pull over, stop, and seek assistance.
How do I check my high-mounted brake light?
Park the vehicle in a safe location and turn on the ignition. Have a helper sit in the driver's seat and apply the brakes while you stand behind the vehicle to observe whether the center high-mounted stop light illuminates. Note any flickering, dimness, or complete darkness.
What does high-mounted brake light mean?
High-mounted brake lights are brake signal lights installed at a higher position on a vehicle. When the driver presses the brake pedal, this light turns on to alert other vehicles to braking, thereby enhancing driving safety.