Why is my collision mitigation braking system light on?

The collision mitigation braking system (CMBS) light indicates the system is unavailable or has detected a fault, and you should not rely on it until it’s checked. Common causes include dirty or obstructed sensors, miscalibration after windshield or front-end work, or a hardware fault.

CMBS uses radar and camera sensors to detect potential collisions and automatically apply braking to reduce crash risk. The warning light can come on for a range of reasons, from simple sensor cleanliness to more complex component failures. This article explains typical causes, what to do immediately, and how to prevent future warnings.

What CMBS is and how it works

Collision mitigation braking systems are driver-assist features designed to help reduce or avoid crashes by automatically braking when a potential collision is detected. They rely on sensors—usually a forward-facing camera and radar or lidar units—and interact with other safety systems like ABS and electronic stability control. While beneficial, CMBS is a assistive technology and not a substitute for attentive driving. When the system detects an issue or cannot operate reliably, the warning light may illuminate.

Common reasons the CMBS warning light comes on

The following list covers the typical situations that trigger the CMBS warning light or cause temporary disablement.

• Sensor obstruction or contamination, such as dirt, snow, ice, or water on the camera or radar sensors, or a dirty windshield.


• Sensor misalignment or front-end damage after a collision or after repaires, which can affect sensor accuracy.


• Calibration needs after windshield replacement or major front-end work; improper calibration can disable CMBS until recalibrated.


• Weather or environmental conditions that degrade sensor performance (heavy rain, fog, snow, or glare). In some cases the system limits operation in poor visibility.


• Faulty sensor, wiring, fuse, or control module within the CMBS hardware or its data bus.


• Software glitches or temporary shutdowns during system checks or during conflicting ADAS operations.


• Electrical issues or low battery voltage that affect sensor power or computer logic.

If the light turns on repeatedly or remains on after addressing obvious cleanliness or alignment issues, it typically indicates a fault that requires diagnostic testing by a qualified technician.

What to do right now

The following steps help you address a CMBS warning promptly while staying safe on the road.

1. Safely pull over and assess the situation if you are driving when the light comes on.


2. Inspect the area in front of the vehicle for obvious obstructions: clean the windshield around the camera area and wipe down the front bumper area where radar sensors may reside.


3. Check for other warning lights or messages on the dash that might indicate battery or ABS issues.


4. Consult the owner’s manual for any manufacturer-specific reset or calibration procedures and any advisories about temporary CMBS operation.


5. Schedule a diagnostic with a trained technician or at a dealership to read fault codes and verify sensor calibration and wiring integrity.


6. Drive with heightened awareness and maintain a greater following distance, ready to brake manually if a collision risk appears.

Concluding paragraph: If cleaning and basic checks don’t clear the warning, or if the light returns, seek professional diagnosis promptly to prevent loss of essential braking assistance.

Why the light might come back after maintenance

After service or calibration, the CMBS light can reappear if any contributing condition recurs or if the system re-detects a fault. The following scenarios are common:

• Sensor calibration required again after windshield work, bumper replacement, or minor front-end impacts.


• Severe weather conditions or new contamination (salt, oil, mud) that temporarily impair sensor performance.


• Wiring or connector issues that re-emerge or develop new faults over time.


• Software updates or a temporary mismatch between modules that triggers a fault code until the system re-stabilizes.

Concluding paragraph: Recurrent warnings after service usually point to a need for a thorough diagnostic and possibly recalibration or component replacement.

Maintenance and prevention tips

The following practices help keep CMBS functioning reliably and reduce false warnings:

• Regularly clean the camera and sensor surfaces and keep the windshield clear of dirt, ice, and streaks that could obscure the camera’s view.


• If the windshield is replaced or major front-end work is performed, request sensor calibration and ensure proper alignment checks are completed by a qualified technician.


• Maintain proper tire condition and alignment, as improper tire wear or misalignment can affect sensor performance and vehicle dynamics used by ADAS.


• Have periodic ADAS diagnostics performed during routine service, especially after impacts or software updates.


• Check for manufacturer-released software updates or recalls that affect CMBS and have them installed at an authorized service center.

Concluding paragraph: Proactive maintenance and timely calibration help keep CMBS reliable and reduce the likelihood of warning lights turning on unexpectedly.

When to seek urgent help

In cases where CMBS warning persists or is accompanied by unusual braking behavior, take these precautions:

1. Do not rely on CMBS; be prepared to brake manually to avoid collisions.


2. If you’re in heavy traffic or an unsafe area, seek roadside assistance or tow the vehicle to a service center if necessary.


3. Schedule an immediate diagnostic if you notice intermittent warnings, reduced performance, or new strange sensor readings.

Concluding paragraph: Persistent or recurrent CMBS warnings warrant prompt professional evaluation to ensure your safety systems are functioning correctly.

Summary

The CMBS warning light signals that the system is either not functioning correctly or is temporarily unavailable due to sensor issues, calibration needs, or hardware faults. Start with a quick check of cleanliness and alignment, then consult your owner’s manual for any reset steps. If the light remains on, have a qualified technician diagnose and recalibrate or replace faulty components. Regular maintenance and sensor care help keep CMBS reliable and reduce false alarms, while driving with extra caution remains essential when the system is not available.

How do I reset my Honda collision mitigation brake system?

To reset a Honda Collision Mitigation Braking System (CMBS) problem, first try turning the vehicle off and on again, as this will often clear temporary glitches. If that doesn't work, you may need to manually turn the system off and then restart it, or for a more complete reset, disconnect the negative battery terminal for a few minutes before reconnecting it. 
Method 1: Restart the vehicle

• This is the simplest first step to try.
• Turn your vehicle completely off.
• Wait for at least a minute.
• Restart the engine and check if the warning light or error message has disappeared. 

This video demonstrates how to reset the collision mitigation system by restarting the car: 57sDashboard warning lights YouTube · Sep 4, 2025
Method 2: Manually turn the system off and on

• CMBS will automatically reset to the "on" position every time you start the engine. 
• Turning it off and then back on can resolve certain errors. 
• To turn it off, press and hold the CMBS OFF button until a beep sounds and the indicator appears. 
• Restart the vehicle to see if the system has been reset. 

Method 3: Disconnect the battery 

• This is a more thorough reset and should be performed with caution.
• Disconnect the negative battery cable.
• Wait a few minutes.
• Reconnect the negative cable.
• Start the car and let it idle for a few minutes before driving. 

This video shows how to disconnect the car battery for a system reset: 58sCarnivautoYouTube · Sep 1, 2025
Important considerations

• If the problem persists after trying these resets, there may be an underlying issue with a sensor or a component that requires professional diagnosis and repair by a dealership. 
• The system can also automatically shut off due to poor weather conditions (like heavy rain or snow) or if the sensors are obstructed. Check for any blockages on the grille and clean the sensors before performing a reset. 
• For a permanent solution to a specific problem, such as a faulty sensor, professional service is recommended. 

What two reasons would cause your brake system warning light to come on?

If your brake service warning light is on, it could indicate hydraulic issues, worn brake pads, or a need for parking brake adjustment. Because the brake service warning light could mean different things, it is best to have a brake specialist diagnose the issue.

Why is my collision mitigation system light on?

The collision mitigation system light is on due to a temporary system issue or a more serious problem with the sensors or radar, often caused by dirt, obstructions, bad weather, or low battery. Start by checking for and cleaning any dirt, snow, ice, or debris from the front sensors and camera, and check your fluids and battery. If the light remains on, it indicates a more significant issue that requires a professional diagnosis.
 
Simple checks and fixes

• Clean the sensors and camera: Obstructions are a common cause. Carefully clean the front grille area and the windshield behind the rearview mirror where the camera is located. 
• Check fluids and battery: A low brake fluid level can trigger these warnings. Also, a weak or failing battery can cause various system warnings to appear, so have your battery tested. 
• Drive in good conditions: The system can temporarily shut off in bad weather, such as heavy rain, fog, or snow, and the light may come on. If the weather improves, the system may reactivate on its own. 
• Check for damage: After a minor front-end collision or even a significant pothole impact, sensors can become misaligned or damaged. Check for any physical damage to the front bumper or grille area. 

When to see a professional

• If the light stays on: If the light remains on after cleaning the sensors and other simple checks, there is likely a persistent fault. 
• Diagnostic scan: A professional mechanic can perform a diagnostic scan to read specific error codes from the system, which will point to a more precise issue. 
• Sensor recalibration: After repairs, sensors often need to be professionally recalibrated to ensure the system works correctly. 
• Faulty components: The problem could be a faulty radar sensor, a damaged camera, or other internal module failure that requires replacement by a certified technician. 

This video demonstrates how to check and clean the sensors and clear the error codes: 57sDashboard warning lights YouTube · Sep 4, 2025

How to fix collision mitigation system problem?

To fix a collision mitigation system problem, first try cleaning the sensors and cameras on the front of your car, as dirt and debris are common causes. Next, ensure your car's battery is fully charged and its connections are secure. If the issue persists, restart the vehicle, or try resetting the system through your car's settings menu. 
Step 1: Clean the sensors and camera

• Clean the radar sensor: Wipe the sensor, which is often located behind the front emblem, with a soft cloth. 
• Clean the windshield camera: Clean the area of the windshield where the camera is located, as smudges can cause issues. 

This video demonstrates how to clean the sensors and camera to fix collision mitigation system problems: 57sDashboard warning lights YouTube · Sep 4, 2025
Step 2: Check the battery 

• Charge the battery: A weak battery can often trigger the warning light. Make sure it is fully charged.
• Secure the connections: Check that the battery terminals are tight and clean. 

Step 3: Reset the system 

• Restart the car: Turn the vehicle off completely, wait about 30 seconds, and then restart it. 
• Reset via settings: Navigate to your car's settings menu, find the driver assistance or safety system setup, and try turning the collision mitigation system off and then back on again. 
• Disconnect the battery (advanced): As a last resort, you can disconnect the negative battery terminal for a few minutes, then reconnect it. This will reset the car's electronics. 

This video shows how to reset the collision mitigation system by disconnecting the battery: 56sCar FixYouTube · Jul 2, 2025
Step 4: Check for other issues

• Check brake fluid: Low brake fluid can sometimes cause warnings for safety systems, so check your fluid levels. 
• Consider alignment: In some cases, a steering wheel that is not centered can cause the system to malfunction. An alignment may be necessary. 
• Consult an expert: If the problem continues, it may be a more complex issue like a faulty sensor or software glitch. You may need to use an OBD2 scanner to read error codes or take the vehicle to a dealer for professional diagnosis.