The little rubber boot that keeps grease in and grit out of a suspension or steering ball joint has split. The joint itself may still be tight today, which is why this is often Minor — but once the boot is open, road grit and water get in and the joint's life is measured in months, not years.
Wording as it commonly appears on an MOT certificate: “Ball joint dust cover damaged or deteriorated so it no longer prevents the ingress of dirt”.
What does it mean?
The little rubber boot that keeps grease in and grit out of a suspension or steering ball joint has split. The joint itself may still be tight today, which is why this is often Minor — but once the boot is open, road grit and water get in and the joint's life is measured in months, not years.
How serious is it?
Usually recorded as: Minor, Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- Age and ozone cracking of the rubber
- Grit blasted up from the road cutting through the folds
- Damage during previous work, often from a joint splitter
- A joint that has been over-greased and burst its own boot
What a mechanic would check
I look for grease flung around the inside of the wheel arch, then squeeze the boot to see if it's split or just dirty. If it's open I check the joint itself for play straight away, because a boot that's been gone a while usually means the joint is already on the way out.
What might need replacing
- A replacement boot kit where the joint is still good and serviceable
- A ball joint
- A complete lower arm on cars where the joint isn't sold separately
- A wheel alignment afterwards
Can you still drive it?
A split boot on a tight joint is safe to drive on while you get it sorted. If the joint has play as well, that's a different story — treat it as urgent.
Repair cost
Boot kits are pennies but only fit where the manufacturer sells the joint separately. On many modern cars the economical fix is the whole arm.
Before the retest
Suspension parts such as springs, shock absorbers and drop links are normally replaced in pairs across an axle so the car sits level and handles evenly. Any work that disturbs the steering or suspension geometry is worth following with a wheel alignment check, otherwise you can pass the retest and still wear out a new pair of tyres within months. Listen for the original knock again on a bumpy road before the retest — if it is still there, something was missed.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More suspension failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.