A warning light related to your blind spot monitoring system has appeared on your dashboard. Maybe it stays on permanently, maybe it appeared after reversing into something, or maybe the small indicator lights in your wing mirrors have stopped working. This guide explains exactly what the blind spot monitoring system does, what the warning light means, and what you should do about it.
What Does the Blind Spot Monitoring Light Look Like
The blind spot monitoring warning light on the dashboard typically shows a car viewed from above or behind with a curved line or dot on one or both sides representing the blind spot zone. It is usually amber or yellow. Some manufacturers use the abbreviation BSM, BSW, or RCTA alongside the symbol.
It is worth knowing that the blind spot monitoring system also has small indicator lights built into or near the wing mirrors themselves. These illuminate in amber when the radar detects a vehicle in the blind spot zone. These mirror indicators are separate from the dashboard warning light. The dashboard light indicates a system fault or disabled state, while the mirror lights are the active alerts during normal operation.
What Is the Blind Spot Monitoring System
The blind spot monitoring system, also known as BSM or blind spot warning, is a driver assistance technology that watches the areas on either side and slightly behind your car that are difficult to see in mirrors. These zones, the blind spots, are where vehicles can sit without being visible in the door mirrors or rear-view mirror.
The system uses small radar sensors, usually mounted in or near the rear bumper on both sides of the car. These sensors continuously scan the zones beside and behind the vehicle while driving. When another vehicle enters the blind spot zone, the system alerts the driver by illuminating a small indicator in the relevant wing mirror. If the driver then activates the turn signal toward that side, the alert becomes more prominent, often flashing the mirror indicator and sounding a warning tone.
The purpose is to reduce the risk of side collisions when changing lanes, which is one of the most common types of motorway accident.
Why the Blind Spot Monitoring Dashboard Light Comes On
Just like the lane departure system, the blind spot monitoring dashboard light can appear for two different reasons.
System Fault or Disabled State When the dashboard light stays on permanently or appears at startup, it means the blind spot monitoring system is either not functioning correctly or has been turned off. This is the situation that may need investigation or a simple reactivation.
Active Alert During Driving The mirror indicator lights activate during normal driving when a vehicle is detected in the blind spot zone. These are the system working correctly and are not a fault. If you see the mirror indicators flashing and hear a tone when you signal a lane change, that is exactly what the system is designed to do.
Common Causes of the Blind Spot Monitoring System Fault
Dirty or Obstructed Rear Bumper Sensors This is the most common cause and also the easiest to fix. The radar sensors are located inside or behind the rear bumper. Mud, dirt, snow, ice, or even a thick layer of road grime over the sensor area can block the radar signal and cause the system to disable itself. Cleaning the rear bumper thoroughly, particularly the corners where the sensors are usually located, often resolves the fault immediately.
Tow Bar or Rear Bike Rack Fitted Attaching a tow bar, a rear bike rack, or any accessory to the back of the car can interfere with the radar sensors. The system may detect the accessory as a constant obstruction and disable itself. Some cars have a setting to deactivate the blind spot system when towing. Others will simply show the fault light until the accessory is removed.
Rear Bumper Damage or Replacement If the rear bumper has been replaced after a collision, the sensors may have been repositioned slightly or the wiring connectors may not have been fully reconnected. Even a minor misalignment of the sensor housing can disrupt the radar signal and trigger the warning light.
Sensor Calibration Required After certain repairs, particularly those involving the rear of the car, the blind spot radar sensors may need to be recalibrated to ensure they are scanning the correct zones. Calibration is done with a specialist scan tool at a garage.
Ice or Snow Covering the Sensors In cold weather, ice buildup on the rear bumper directly over the sensor locations can block the radar. The system will disable and the warning light comes on. In most cases the light clears on its own once the ice has melted or been removed. Do not use sharp tools to remove ice from the bumper as this can damage the sensor housing.
Wiring or Connector Fault Corrosion or damage to the wiring that connects the radar sensors to the system control module can cause a fault. This is more common on older vehicles or those that have been in a rear collision. A diagnostic scan is needed to identify this type of fault.
System Manually Turned Off Many cars allow the driver to disable the blind spot monitoring system through a button or through the driver assistance settings menu. If a previous driver turned it off, the dashboard indicator may stay on as a reminder. Check your car manual for how to reactivate the system.
How Serious Is This Light
The blind spot monitoring system is a driver assistance feature, not a safety-critical mechanical system. The car is completely safe to drive without it functioning. However, the system exists because blind spot collisions are a genuine and common road hazard, particularly on motorways and dual carriageways when changing lanes at speed.
If you drive regularly on busy roads or motorways, having the blind spot monitoring system working correctly gives you an additional layer of protection that is worth maintaining.
For most drivers this is not an urgent repair but it should be investigated, particularly if the cause is something simple like a dirty bumper or a setting that was accidentally changed.
What To Do When the Blind Spot Monitoring Light Stays On
Step 1: Check whether the system was manually turned off. Look for a BSM or blind spot button on the dashboard or steering wheel, or check the driver assistance settings in the infotainment menu. Reactivate it if it was disabled.
Step 2: Check the rear bumper corners for mud, dirt, snow, or ice covering the sensor areas. Clean the bumper thoroughly and check if the light clears.
Step 3: If a tow bar, bike rack, or any rear-mounted accessory is fitted, remove it and check if the light goes off. If it does, the accessory was interfering with the sensors.
Step 4: Check whether the rear bumper has recently been repaired or replaced. If so, the sensors may need to be recalibrated or the wiring checked.
Step 5: If none of the above apply, get a diagnostic scan to read the specific fault code stored in the system. This will identify whether the fault is in a sensor, the wiring, or the control module.
Step 6: If the light appeared after cold weather and has now cleared on its own as the car warmed up, ice over the sensors was likely the cause. No further action is needed unless it happens regularly.
Can You Drive With the Blind Spot Monitoring Light On
Yes. The car is mechanically safe to drive. The blind spot monitoring system is a driver assistance feature and its absence does not prevent the car from operating safely.
However, while driving without the system active, be extra careful when changing lanes. Check your mirrors thoroughly and physically turn your head to check the blind spot before signalling and moving, particularly on motorways where vehicles can approach quickly from behind.
Blind Spot Monitoring Light vs Mirror Indicator Lights
Many drivers confuse these two different indicators. Here is the clear difference:
The dashboard warning light in amber that stays on means the system has a fault or has been disabled. It is not actively monitoring your blind spots.
The small amber lights in the wing mirrors that illuminate briefly when a vehicle is detected beside you are the active alerts. These mean the system is working perfectly and a vehicle is present in the blind spot zone right now. If these mirror lights flash when you indicate a lane change, do not change lanes until they go off.
How To Turn Off Blind Spot Monitoring
If the system alerts too frequently or you want to disable it temporarily, most cars allow this through a BSM button on the dashboard or through the driver assistance settings in the infotainment menu. The method varies by manufacturer. Check your car manual for the specific steps for your vehicle.
On some cars disabling the system causes the dashboard warning light to remain on as a reminder. This is normal and not a fault indicator when the system has been manually turned off.
Quick Summary
What | Detail |
Light Color | Amber or Yellow |
Symbol | Car outline with curved lines or dots on the sides |
Severity | Low for vehicle safety, worth investigating |
First Check | Clean rear bumper sensors, check if system was manually disabled |
Most Common Cause | Dirty sensors, ice on bumper, tow bar interference, system turned off |
Risk if Ignored | Loss of blind spot protection when changing lanes |
Related Warning Lights
These warning lights are also part of the safety and driving assistance systems on modern cars:
- Lane Departure Warning Light – Forward camera system for lane drift alerts
- Brake Warning Light – Safety critical braking system fault
- Power Steering Warning Light – Steering assistance fault affecting vehicle control
- Reduced Engine Power Light – Engine management fault limiting performance
This page is part of our complete guide to car dashboard symbols and meanings. To see every warning light explained in one place, visit our Car Dashboard Symbols.