Why has my car sunk overnight?

An air leak, almost certainly. Air springs are rubber bellows that perish with age and split along the fold where they roll, and once there is a leak the car will settle while it is parked and the compressor is not running. It usually shows up on one corner first. The other common sources are a leaking valve block, which lets air escape from a specific corner even when the spring is sound, and a corroded air line. A car that sinks overnight but rises again in the morning is still leaking — the compressor is simply refilling it — and leaving it that way is what kills compressors.

Can I drive with the air suspension warning light on?

Only as far as a garage, and only if the car is still sitting at something like a normal height. Most systems will keep the car up in a limited mode and cap your speed. If the car has settled onto its bump stops, do not drive it: the correct ride height is what keeps driveshaft angles, brake pipes and the underside of the body clear, and running on the stops causes damage well beyond the suspension itself. Be aware the situation can change while the car is parked, so a car that drove home fine may be on the floor the next morning.

Does air suspension fail an MOT?

Not for the warning lamp, which is not a listed defect. It fails for the physical consequences. A split or badly deteriorated air spring, a corroded mounting or a damaged component is recordable under section 5.3, mostly as a major defect. A car that cannot reach normal ride height may not be able to complete the underside inspection or the brake test at all. And because self-levelling headlamps usually take their signal from the ride height sensors, an air suspension fault frequently drags a headlamp levelling failure along with it, which is a major defect under section 4.1.5.

Should I convert my air suspension to coil springs?

It is a common choice on older cars where the whole system is tired, and it does make the car predictable again, but there are real trade-offs. Conversion kits usually leave the control module with no sensors to read, so you can be left with a permanent warning lamp unless a bypass module is fitted. You lose self-levelling, which matters if you tow or carry loads, and on cars whose headlamps level from the ride height sensors you can create a headlamp aim problem that is itself an MOT failure. The ride will not be what the car was designed around either. Where only one spring has failed on an otherwise healthy system, replacing that spring is usually the better answer.

Dashboard warning light

Air suspension warning light

Last updated 27 July 2026

Quick answer

The air suspension has a fault and can no longer hold or adjust ride height reliably. The classic sign is a car that has sunk on one corner or at one end overnight, or one that refuses to rise and limits your speed until it does.

What to do: Get it checked within days
Can you drive?: Only to a garage

Why it is amber

A system has reported a malfunction, or something needs attention. The car is usually still driveable, but the fault will not clear itself and several amber lamps are an automatic MOT failure.

What turns it on

Air suspension replaces steel springs with rubber air springs, kept at pressure by a compressor and controlled through a valve block using ride height sensors at each corner. Almost every fault starts as a leak: the rubber bellows perish and split with age, most often where they fold, and the compressor then runs more and more often to keep up. Eventually it cannot keep up, or it burns out from the constant duty, and the system gives up and warns you. Leaking valve blocks, corroded air lines and failed height sensors account for most of the rest.

What to do about it

Deal with it quickly rather than living with it. A small leak makes the compressor run almost constantly, and a burnt-out compressor turns a modest repair into a much dearer one. This is the rare case where prompt action genuinely saves money.
Listen for the compressor. One that runs for a long time after starting, or cycles repeatedly while parked, is confirming a leak before you can see anything wrong.
Try spraying soapy water around the air spring folds and the pipe unions with the car at normal height. A split bellows will usually give itself away.
Do not jack the car up without checking the handbook. Many air-sprung cars need the system placing in a jacking or service mode first, and lifting one wheel with the system live can make it fight you or damage a component.
If the car has settled on its bump stops, do not drive it. The ride height is a structural assumption on these cars and driving on the stops damages far more than the suspension.
Have the headlamp aim checked after any repair. Self-levelling headlamps take their reference from the ride height sensors, so a suspension fault and a headlamp levelling fault frequently arrive together.

Can you keep driving?

Only to a garage

It depends how far the car has dropped. Sitting slightly low with the lamp on, most cars will put themselves into a limited mode and get you to a garage. A car resting on its bump stops should not be driven at all: the ride height is what keeps driveshaft angles, brake lines and the underside of the car where they are meant to be, and running on the stops does expensive damage very quickly. Bear in mind that these systems often deflate overnight, so a car that was fine on the way home may be sitting on the floor in the morning.

What causes it

A perished or split air spring, which is the overwhelmingly common cause and simply a function of age
A worn compressor, often with a failed piston seal or a blocked drier, which cannot build pressure any more
A leaking valve block, which typically shows up as one specific corner sinking
Corroded or chafed air lines, particularly where they run along the underside and through the wheel arches
A failed ride height sensor or a snapped plastic sensor link
A relay or fuse for the compressor, which is worth checking before condemning anything expensive
Cold weather, which stiffens perished rubber and makes a marginal system fail on the first frost of the year

Does it fail an MOT?

Not on its own — but what causes it often does.

There is no MOT defect for the air suspension warning lamp itself. The consequences of the fault are very much in the test though. Under section 5.3 the tester records damaged, deteriorated or insecure suspension components, corroded mountings and anything fractured or excessively worn, so a split air spring or a corroded mounting is a recordable defect. A car that cannot be raised to its normal ride height also causes practical problems: the underside inspection and the brake test may not be possible, and a test that cannot be completed is not a pass. Because self-levelling headlamps usually take their reference from the ride height sensors, an air suspension fault often brings a headlamp aim or levelling failure with it, and an inoperative headlamp levelling device is a major defect under section 4.1.5.

Common questions

Why has my car sunk overnight?: An air leak, almost certainly. Air springs are rubber bellows that perish with age and split along the fold where they roll, and once there is a leak the car will settle while it is parked and the compressor is not running. It usually shows up on one corner first. The other common sources are a leaking valve block, which lets air escape from a specific corner even when the spring is sound, and a corroded air line. A car that sinks overnight but rises again in the morning is still leaking — the compressor is simply refilling it — and leaving it that way is what kills compressors.
Can I drive with the air suspension warning light on?: Only as far as a garage, and only if the car is still sitting at something like a normal height. Most systems will keep the car up in a limited mode and cap your speed. If the car has settled onto its bump stops, do not drive it: the correct ride height is what keeps driveshaft angles, brake pipes and the underside of the body clear, and running on the stops causes damage well beyond the suspension itself. Be aware the situation can change while the car is parked, so a car that drove home fine may be on the floor the next morning.
Does air suspension fail an MOT?: Not for the warning lamp, which is not a listed defect. It fails for the physical consequences. A split or badly deteriorated air spring, a corroded mounting or a damaged component is recordable under section 5.3, mostly as a major defect. A car that cannot reach normal ride height may not be able to complete the underside inspection or the brake test at all. And because self-levelling headlamps usually take their signal from the ride height sensors, an air suspension fault frequently drags a headlamp levelling failure along with it, which is a major defect under section 4.1.5.
Should I convert my air suspension to coil springs?: It is a common choice on older cars where the whole system is tired, and it does make the car predictable again, but there are real trade-offs. Conversion kits usually leave the control module with no sensors to read, so you can be left with a permanent warning lamp unless a bypass module is fitted. You lose self-levelling, which matters if you tow or carry loads, and on cars whose headlamps level from the ride height sensors you can create a headlamp aim problem that is itself an MOT failure. The ride will not be what the car was designed around either. Where only one spring has failed on an otherwise healthy system, replacing that spring is usually the better answer.

This is general guidance, not a diagnosis. Manufacturers draw the same system differently and reuse symbols for more than one function, so check the handbook for your own car before acting on anything here.

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