Car Modifications That Can Cause MOT Failure

Understanding which modifications can fail your MOT test and result in expensive repairs or fines

Important Warning: Over 7 million vehicles fail their MOT annually - many due to illegal modifications

Why Car Modifications Can Cause MOT Failures

A car owner may choose to modify their vehicle to improve its appearance or performance. However, despite the attractiveness of some car modifications, not all meet legal requirements.

There are popular modifications motorists like to make, such as louder speakers for their stereo or tinted windows to stop the glare of the sun. However, an illegal modification might result in your vehicle failing an MOT or potentially resulting in an on-the-spot penalty.

Penalties for Illegal Modifications

A £1,000 fine may be levied if caught driving without an MOT. You can still be fined up to £2,500 if your vehicle is considered unsafe, plus three points on your license.

Common Modifications That Can Cause MOT Failure

One of the most common reasons for a car to fail its MOT is due to modifications. If your car has been modified in any way, it could be deemed unsafe and fail its MOT. Some of the most common modifications include:

Changing the Suspension or Wheels

Lowered suspension or oversized wheels that affect handling, clearance, or speedometer accuracy can fail MOT inspection.

Adding Aftermarket Exhausts or Intakes

Modified exhaust systems that exceed noise limits or affect emissions can result in immediate failure.

Upgrading the Engine

Engine modifications that increase emissions beyond legal limits or affect safety systems will fail inspection.

Adding Aftermarket Body Kits or Spoilers

Body modifications with sharp edges, loose fittings, or that obscure lights can be deemed unsafe.

Important: If you have made any of these modifications to your car, it is important to have them reversed or made compliant before taking your car in for its MOT. Otherwise, you are likely to fail the test and be required to make expensive repairs.

Simple Accessories That Can Cause MOT Failure

In addition to car modifications, simple car accessories can also cause an MOT failure, as well as possible fines. According to the most recent DVSA data, over 7 million automobiles fail their MOT each year, and it's not always due to major vehicle issues.

Driver's View Obstructions

8% of MOT failures are due to problems with the driver's view to the road - a potentially costly mistake.

Dashcams & Sat-Navs

Dashcams and sat-navs stuck in the wrong place can obstruct the driver's view and cause MOT failure.

Hanging Accessories

Dream catchers, air fresheners, or any items hanging from the rear-view mirror can obstruct vision.

Tinted Windows

Excessively tinted windows that don't meet legal light transmission requirements will fail inspection.

Do I Have to Declare Modifications?

Yes, you must declare modifications to your insurance company. Failing to declare modifications can invalidate your insurance policy, leaving you without cover in the event of an accident.

Modifications That Must Be Declared:

  • Engine modifications or upgrades
  • Suspension changes
  • Wheel or tyre size changes
  • Body kit additions
  • Exhaust system modifications
  • Window tinting

Potential Penalties

£1,000

Fine for driving without valid MOT

£2,500

Fine for unsafe vehicle condition

3 Points

License penalty points

Additional Penalty: If you've been convicted of driving an unsafe vehicle in the previous three years, you could be banned from driving for at least six months.

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