Will my horn fail my MOT? 

Thursday 11th June 2026

Your car horn is easily overlooked when getting ready for your MOT. An MOT tester will sound your horn during the test to check it works correctly. If it fails to sound, continues to sound after releasing the horn, or is wired incorrectly, your vehicle will fail its MOT. The horn is a legal requirement for all vehicles under the Road Vehicles Regulations 1986 and must work to pass your MOT. 

What does an MOT tester check the horn for?  

The horn must produce a continuous, uniform sound and be loud enough to be heard by other road users. Novelty horns, like one that plays a musical tune, are not allowed and will fail. A horn that cuts in and out, or fails to respond immediately, will also fail. 

Common reasons for failure 

If the horn is sounded but produces no noise, it is usually due to a blown fuse, faulty relay, or corroded earth connection. If it works intermittently, the horn unit could be corroded or damaged. On most vehicles, the horn sits behind the front bumper, which takes the worst of road spray, salt, and debris. A weak or quiet sound could mean the horn diaphragm is worn out and needs replacing. 

How to fix horn issues 

If you check the horn before your MOT and find an issue, start by checking the fuse box. If the fuse is fine, check the relay. How to check these will depend on the make and model of your vehicle and will be listed in your vehicle's handbook. If the diaphragm is worn out, a new horn is relatively inexpensive and easy to fit at home. Replacing it before your MOT avoids an avoidable failure and the cost of a retest. 

How long should a horn last? 

Most horn units last the life of the vehicle, although premature failure can happen, usually due to water damage or corrosion, particularly on vehicles that cover high mileages in wet conditions. 

How can Formula One Autocentres help? 

Once you’re ready and prepped, book your MOT and service together to save; an MOT booked together with a service starts from £29.50. Use our branch finder to find your nearest Formula One Autocentres branch today.