Blind Spot Monitor Warning Light

Can I keep driving?

What to do right now

1. 1Rely strictly on your wing mirrors and look over your shoulder before changing lanes or joining motorways.
2. 2Check whether heavy spray, mud, road salt or packed snow is coating the corners of your rear bumper.
3. 3Pull into a safe car park or service station to wipe the rear bumper corners clean with a soft cloth.
4. 4Switch off the engine for two minutes and restart it to see if the warning system resets.

Likely causes

Most likely first.

1. Likely

   Dirt, road salt or snow on the rear bumper

   The radar units sit behind the outer plastic corners of the rear bumper and need a clear line of sight. A thick crust of grime, slush or mud absorbs the radar waves, forcing the computer to disable the system for safety.

2. Possible

   Radar sensor misaligned from a minor knock

   A gentle bump in a car park or a tap to the rear bumper can bend the internal mounting bracket by just a few degrees. If the radar points slightly off target, the control module detects the error and shuts the system down.

3. Possible

   Corroded wiring harness or plug connector

   Mounted low behind the rear wheels, the sensors endure continuous road spray, grit and winter salt. Water can seep into the multi-pin plugs over time, causing broken signals or short circuits.

4. Possible

   Failed radar control module

   Internal electronic components can suffer water ingress or circuitry failure after years of road vibration. When the module stops communicating with the car network, a permanent warning light appears.

5. Rare

   Towing a trailer or carrying bicycles

   Bicycle racks or trailers cover the radar field and trick the system into sensing a permanent obstruction. Most vehicles detect a trailer plug in the tow socket and shut the monitor off automatically.

What you can check yourself

Park somewhere safe and level, engine off, before you start.

1. 1

   Clean the rear bumper corners

   Locate the curved outer corners of your rear bumper where the radar units sit underneath. Wash away any road film, caked mud or ice with warm soapy water and dry the area thoroughly.

2. 2

   Check the dashboard settings menu

   Use your steering wheel buttons to scroll into the driver assistance menu on the instrument display. Confirm that the blind spot monitor has not been turned off accidentally or set to trailer mode.

3. 3

   Inspect the bumper for cracks or misalignment

   Examine the rear corners for scuffs, popped clips or uneven panel gaps from a recent bump. If the bumper cover is deformed, the radar bracket underneath is likely twisted out of its calibrated position.

4. 4

   Remove tow-bar accessories

   Disconnect any bike racks, luggage carriers or trailer electric plugs attached to the rear of the car. If the light goes out once the rear area is clear, the system is working exactly as designed.

5. 5

   Perform an ignition restart

   Park on level ground, turn the ignition completely off, take the key out and wait two minutes before starting the engine. This gives the body control module time to reboot and clear temporary software flags.

Typical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. The total repair bill depends heavily on whether the sensor simply needs recalibration using specialist garage targets or must be replaced with a costly genuine radar unit.

When to go to a garage

• The warning light stays lit after washing the bumper thoroughly and restarting the vehicle.
• The fault began straight after a car park bump, minor collision or bodywork repair.
• The system gives false alarms, flashing constantly when there are no vehicles or barriers nearby.
• A scan shows lost communication codes that do not clear after a full system reset.

Questions drivers ask

Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.