A UK driver's guide to dashboard warning lights: what red, amber and green mean, which lights mean stop now, and what to do next.
Most dashboard lights are not emergencies, but a few really are, and the hard part is telling them apart at 60 mph. This guide explains the colour system that almost every manufacturer uses, the lights that mean you should stop as soon as it is safe, the ones that can wait for a garage visit, and the steps to take in each case. Symbols differ a little between makes, so your handbook is always the final word for your car.
The colour code: red, amber, green and blue
Car makers follow a broadly traffic-light system, set out in international standards for vehicle controls and tell-tales:
- Red: a serious problem or a safety issue. Stop as soon as it is safe to do so and find out what is wrong before you carry on.
- Amber or yellow: something needs checking soon. You can usually keep driving carefully, but book it in rather than ignoring it.
- Green or blue: information only. A system is switched on, such as dipped headlights (green) or main beam (blue).
A light that flashes is usually more urgent than the same light shown steadily. A flashing engine management light, for example, often means the engine is misfiring badly enough to damage the catalytic converter.
Lights that mean stop as soon as it is safe
Oil pressure (red oil can)
This warns that oil pressure has dropped, not just that the level is a little low. Without pressure the engine's moving parts are not lubricated and serious damage can follow within minutes. Pull over safely, switch off and check the level with the dipstick once the car has stood for a few minutes. If the level is fine and the light stays on, do not drive it: call for recovery.
Coolant temperature (red thermometer)
The engine is overheating. Stop, switch off and let it cool. Never open the coolant cap on a hot engine: the system is pressurised and can spray scalding liquid. Once it is cold, check the level against the marks on the expansion tank.
Brake system (red circle with an exclamation mark)
First check the parking brake is fully released. If it is, the light can mean low brake fluid or a fault in the system. Brakes are not something to gamble on: get it checked before driving any distance.
Charging or battery (red battery)
The battery is not being charged, often because of an alternator or drive-belt fault. The car will run on stored charge for a short time, then electrics and eventually the engine will fail. Switch off non-essential electrics and head straight for a safe place or a garage.
Power steering
Steering may become very heavy, especially at low speed. Drive slowly to a safe stop and get it looked at.
Amber lights: get it checked soon
Engine management light (amber engine outline)
The car's computer has logged a fault with the engine or emissions system. It could be anything from a loose fuel cap to a failing sensor. A steady light means book it in; a flashing light means reduce speed and get it checked promptly. Since the MOT changes of 20 May 2018, an illuminated engine management light is a major defect, so the car will fail its MOT while it is on.
ABS (amber "ABS" in a circle)
Your normal brakes still work, but the anti-lock function that stops wheels locking under hard braking may not. Leave more room and get it checked.
Airbag or SRS (amber seated figure with a circle)
An airbag or seatbelt pre-tensioner may not deploy in a crash. It is also an MOT failure.
Tyre pressure monitoring (amber horseshoe with an exclamation mark)
One or more tyres has lost pressure. Check all four, including for punctures, and reset the system as your handbook describes. On cars first used from 1 January 2012, a fault with the tyre pressure monitoring system is checked at the MOT.
Traction or stability control (car with wavy lines)
Flashing briefly on a slippery road is normal: it means the system is working. If it stays on, the system may be switched off or faulty.
Diesel-specific lights
Diesels can show a glow-plug light (a coil symbol), a diesel particulate filter light and an AdBlue warning. Each needs a different fix: a particulate filter light usually means the filter needs a sustained run to clean itself (your handbook gives the exact advice), while an AdBlue warning means the tank needs topping up before the range countdown reaches zero, after which most cars will not restart.
What to do when a light comes on: step by step?
- Note the colour and whether it flashes. Red or flashing means act now.
- Check how the car feels. Loss of power, smoke, new noises, smells or heavy steering all raise the urgency.
- Stop somewhere safe if needed. On a motorway, use an emergency area or the hard shoulder only in a real emergency, as the Highway Code advises, and leave by the nearside doors.
- Look the symbol up in your handbook. Many makers publish handbooks online if you have lost yours.
- Do the simple checks that are safe to do: oil level, coolant level when cold, tyre pressures, fuel cap.
- Get a diagnosis. A garage can read the fault codes stored by the car; a basic code reader can also do this at home.
Warning lights A to Z
Every common dashboard light, what it means and whether you can keep driving. Symbols vary slightly between makes, so always check your owner's handbook.
- ABS warning light: can you still brake?
- AdBlue warning light
- Airbag (SRS) warning light
- Battery and charging warning light
- Brake pad wear warning light
- Brake warning light: the handbrake symbol that is not always the handbrake
- Buying a used car? Check the dashboard warning lights first
- Diesel particulate filter (DPF) warning light
- Digital dashboards: how warnings work on a digital instrument display
- Door, bonnet and boot open warning lights
- Driver assistance warnings: lane assist, emergency braking and cruise
- Engine management light (check engine): what it means
- Engine temperature warning light: what to do if your car overheats
- Exterior bulb failure warning light
- Gearbox and transmission warning lights
- Key, immobiliser and security warning lights
- Low fuel warning light: how far can you go?
- Oil pressure vs oil level warning lights: the difference
- Power steering warning light
- Seatbelt reminder light and chime
- Service due indicator: what the spanner light means
- The snowflake (frost) warning light
- Traction control and stability control (ESC) lights
- Tyre pressure (TPMS) warning light
- Warning light on the motorway: what to do
- What warning lights really cost: why acting early is cheaper
- Which dashboard warning lights fail an MOT?
ABS warning light: can you still brake?
The amber ABS light means anti-lock braking is not working. Normal brakes should still work, but here is what to watch for and how it affects the MOT.
The anti-lock braking system has a fault and is switched off. Normal braking usually still works, but wheels can lock in an emergency stop.
What it looks like
The letters ABS in a circle. Colour: Amber.
Common causes
- Faulty wheel speed sensor (very common)
- Damaged sensor wiring
- ABS pump or module fault
- Low battery voltage
What to do
- Drive carefully and leave extra stopping distance, especially in the wet.
- If the red brake light comes on as well, stop: it may be a more serious brake fault.
- Have it diagnosed. A wheel speed sensor is often an affordable fix.
Can I keep driving?
Yes, with care, if only the ABS light is on.
MOT
An ABS warning light showing a fault is an MOT fail.
AdBlue warning light
Diesels with SCR need AdBlue. What the warning means, how to top up and why the car may refuse to start if it runs out.
AdBlue (diesel exhaust fluid) is running low or the system has a fault.
What it looks like
A fluid can or the letters AdBlue or DEF. Colour: Amber, turning red.
Common causes
- Low AdBlue level
- Crystallised AdBlue or a faulty pump or sensor
What to do
- Top up with AdBlue to ISO 22241 standard; it is sold at most fuel stations.
- Never put AdBlue in the fuel tank.
- Most cars give a countdown of miles; once it reaches zero, the car may not restart until topped up.
Can I keep driving?
Yes until the countdown ends.
MOT
Not directly, but emissions faults can cause a fail.
Airbag (SRS) warning light
An airbag light that stays on means the airbags may not deploy in a crash. Common causes and why it should be fixed promptly.
The supplementary restraint system (airbags and seatbelt pretensioners) has a fault and may not work.
What it looks like
A seated person with a circle in front, or SRS. Colour: Red or amber.
Common causes
- Faulty seat wiring connector, often after seats are moved
- Clock spring fault in the steering wheel
- A previous crash or failed sensor
- Low battery voltage during starting
What to do
- The car will still drive normally, but get it checked soon.
- Do not try to remove airbags yourself; they are explosive devices.
- A garage with the right diagnostic tools can read the fault.
Can I keep driving?
Yes, but your airbags may not protect you until it is fixed.
MOT
An airbag warning light that shows a fault is an MOT fail.
Battery and charging warning light
The red battery light usually means the car is not charging its battery, not that the battery is flat. Causes and what to do.
The charging system is not keeping the battery charged while the engine runs.
What it looks like
A battery with + and − symbols. Colour: Red.
Common causes
- Failed alternator
- Broken or slipping auxiliary (alternator) belt
- Loose or corroded battery terminals
- Wiring faults
What to do
- Switch off non-essential electrics (heated seats, rear screen heater, stereo).
- Drive to a safe place or garage nearby without switching off, because the car may not restart.
- If the belt has snapped, it may also drive the water pump or power steering, so stop and call for help.
Can I keep driving?
Only a short distance to safety.
MOT
Not an MOT item, but the battery must be secure and terminals sound.
Brake pad wear warning light
A circle with dashed lines on each side means your brake pads are worn. How long you have and why you should not delay.
The brake pad wear sensor has detected that pads are close to their minimum thickness.
What it looks like
A circle between two dashed curved brackets. Colour: Amber.
Common causes
- Worn brake pads
- A damaged wear sensor wire
What to do
- Book new pads (and usually a new sensor) soon.
- Listen for grinding: metal on metal means pads are fully worn and discs will be damaged.
- Have the discs checked at the same time.
Can I keep driving?
Yes, for a short time, but book a replacement promptly.
MOT
Brake pads below the minimum thickness, or a pad wear warning, can be an MOT fail.
Brake warning light: the handbrake symbol that is not always the handbrake
The red brake warning light can mean the parking brake is on, brake fluid is low or there is a brake system fault. How to tell the difference.
Either the parking brake is applied, or the brake fluid level is low, or the brake system has a fault.
What it looks like
A circle inside brackets with an exclamation mark, or the letter P. Colour: Red.
Common causes
- Parking brake not fully released
- Low brake fluid (often from worn pads or a leak)
- Electronic parking brake fault
What to do
- Check the parking brake is fully off.
- If it stays on, stop safely and check the brake fluid reservoir level.
- Low brake fluid can mean a leak: do not drive until checked.
Can I keep driving?
No, unless it is only the parking brake reminder.
MOT
Brake system warning lights indicating a fault are an MOT fail.
Buying a used car? Check the dashboard warning lights first
Six quick dashboard checks before buying a used car in the UK: the bulb test, a cold start, MOT history, fault codes and recalls.
Dashboard lights are one of the quickest clues to a used car's condition. A few checks before you buy can save a lot of money.
1. Check the bulb test
Turn the ignition on without starting the engine. Most warning lights, including engine, ABS, airbag and oil, should light up briefly. If one does not, the bulb may have been removed or the cluster tampered with to hide a fault.
2. Start from cold
Ask for the engine to be cold when you arrive. Watch all the lights go out after starting. Some faults only show when cold.
3. Test drive long enough
Drive for at least 20 minutes, including faster roads if you can. Some faults, such as DPF or gearbox problems, only appear once things warm up.
4. Look at the MOT history
The free GOV.UK MOT history service shows past failures and advisories, such as an ABS or airbag light. Repeated advisories for the same thing are a warning sign.
5. Ask for a code scan
A garage or a mobile inspector can scan for stored fault codes. Recently cleared codes, shown by incomplete readiness monitors, can mean a seller has hidden a problem.
6. Check recalls
Use the GOV.UK recall checker to see whether any safety recalls are outstanding.
If a light is on
Do not accept "it's just a sensor". Ask for a written diagnosis, a price reduction to cover the repair, or walk away. Buying from a dealer gives you more rights under the Consumer Rights Act 2015 than a private sale.
Diesel particulate filter (DPF) warning light
The DPF light means the filter in a diesel exhaust is getting blocked. How regeneration works and what driving helps clear it.
Soot has built up in the diesel particulate filter and it needs to regenerate (burn off the soot).
What it looks like
A box with dots inside, shaped like an exhaust filter. Colour: Amber.
Common causes
- Lots of short, low-speed journeys
- Sensor faults
- Engine problems causing excess soot
What to do
- Follow your handbook. Many recommend a sustained drive at a steady speed on a dual carriageway or motorway to allow regeneration.
- If the light stays on or the car goes into reduced power, see a garage.
- Do not remove the DPF: it is illegal to drive a car that had one fitted without it, and it will fail the MOT.
Can I keep driving?
Yes, generally, but act soon.
MOT
Visible smoke or a removed DPF is an MOT fail.
Digital dashboards: how warnings work on a digital instrument display
How warning lights and messages work on digital instrument clusters, and how to find warnings you have dismissed.
Many newer cars have a fully digital instrument display instead of physical dials. It changes how warnings are shown, but not what they mean.
What is different
- Text with symbols. Digital displays often add a message such as "Engine fault: drive with care", which is clearer than a symbol alone.
- Priority pop-ups. Red warnings may take over the screen; amber ones may appear briefly then sit in a menu.
- Message history. Many cars keep a list of current warnings in the vehicle settings or a "vehicle status" menu.
Things to watch out for
- Dismissed messages can disappear while the fault remains. Check the status menu.
- Customised layouts (maps, music) can hide gauges such as coolant temperature. The warning lights still appear.
- Software updates can change how messages look.
What stays the same
The colour rules still apply: red means stop when safe, amber means check soon, and green or blue are information. MOT rules on warning lights apply whether the display is digital or analogue.
Tip
Spend ten minutes with the handbook learning where warnings and the vehicle status menu appear on your car's display.
Door, bonnet and boot open warning lights
A car with open doors on the dashboard means a door, bonnet or boot is not fully latched. Why it matters and what to do if it stays on.
A door, the bonnet or the boot lid is not fully closed, or its switch is faulty.
What it looks like
A car seen from above with doors open, or a car with the bonnet or boot raised. Colour: Red or amber.
Common causes
- A door, boot or bonnet not fully latched
- A faulty door switch or latch sensor
- Dirt or ice in the latch
What to do
- Stop safely and check every door, the boot and the bonnet.
- An unlatched bonnet can fly up at speed and block your view: never drive with the bonnet warning on.
- If everything is shut, the latch switch may need cleaning or replacing.
Can I keep driving?
Not until you have checked; never with an unlatched bonnet.
MOT
Doors must open and close properly from inside and outside for the MOT; a bonnet that will not latch is a fail.
Driver assistance warnings: lane assist, emergency braking and cruise
Warnings for lane-keeping, autonomous emergency braking and adaptive cruise often mean a sensor is blocked. How to clear them and when to worry.
A camera or radar used by a driver assistance system is blocked or faulty, so the system is unavailable.
What it looks like
Symbols such as a car between lane lines, a car with radar waves, or a speedometer with a car. Colour: Amber.
Common causes
- Dirt, snow, ice or insects on the windscreen camera area or front radar sensor
- Heavy rain or low sun
- A recent windscreen replacement without camera recalibration
- Sensor fault or damage after a bump
What to do
- Clean the windscreen in front of the camera and the badge or grille area where the radar sits.
- If a windscreen has been replaced, ask the fitter to confirm the camera was recalibrated.
- If it stays on in good conditions, have the system checked.
Can I keep driving?
Yes. Drive normally without the assistance system.
MOT
Not a standard MOT test item at present.
Engine management light (check engine): what it means
The amber engine-shaped light means the engine computer has logged a fault. Steady versus flashing, common causes, what to do and MOT rules.
The engine control unit has detected a fault in the engine, emissions or ignition system and stored a fault code.
What it looks like
An engine outline, sometimes with the word CHECK. Colour: Amber.
Common causes
- Faulty oxygen (lambda) sensor
- Loose or worn fuel cap seal
- Ignition coil or spark plug faults (misfires)
- Exhaust gas recirculation (EGR) valve or DPF problems on diesels
- Mass airflow sensor faults
What to do
- If it is steady, drive gently and book a diagnostic check soon.
- If it is flashing, the engine is usually misfiring badly: reduce speed and stop when safe, because unburnt fuel can damage the catalytic converter.
- A garage, or a basic OBD-II code reader, can read the stored code. The code points to the system, not always the exact part.
Can I keep driving?
Usually yes if steady and the car drives normally; no if flashing or the car is losing power.
MOT
An illuminated engine management light is a major fault and an MOT fail.
Engine temperature warning light: what to do if your car overheats
The red thermometer light means the engine is too hot. Safe steps to take, why you must not open a hot radiator cap and common causes.
Coolant temperature is too high, so the engine is at risk of overheating.
What it looks like
A thermometer in wavy lines (liquid). Colour: Red (some cars show blue when the engine is cold).
Common causes
- Low coolant from a leak
- Failed thermostat or water pump
- Cooling fan not working
- Blocked radiator
What to do
- Pull over safely and switch off the engine.
- Do not open the coolant cap while hot: pressurised coolant can scald.
- When cool, check the coolant level against the marks on the expansion tank and top up with the correct coolant if needed. If it keeps happening, get it inspected.
Can I keep driving?
No. Driving an overheating engine can warp the cylinder head.
MOT
Not a direct MOT item, but coolant leaks may be noted.
Exterior bulb failure warning light
A light bulb symbol with an exclamation mark means an exterior lamp has failed. How to find which bulb, the law and the MOT.
One of the exterior lights, such as a brake light, indicator or headlight, has failed or has a wiring fault.
What it looks like
A light bulb with an exclamation mark, or a lamp symbol. Colour: Amber.
Common causes
- Blown bulb
- Corroded bulb holder or connector
- Wrong bulb type fitted
What to do
- Walk round the car with lights, indicators and brakes on (ask someone to press the brake, or use a reflection).
- Replace the bulb with the correct type from the handbook. Many LED units need a garage.
- Drivers must keep lights working; police can stop you for defective lights.
Can I keep driving?
Yes, but fix it quickly, especially brake lights and headlights.
MOT
Lamps that do not work are an MOT fail.
Gearbox and transmission warning lights
A gear symbol or a thermometer-in-gear light warns of an automatic gearbox fault or overheating. What to do and limp mode explained.
The automatic gearbox or transmission has a fault or is overheating. The car may enter 'limp mode', holding one gear to protect itself.
What it looks like
A cog wheel, sometimes with an exclamation mark or thermometer. Colour: Amber or red.
Common causes
- Overheating in heavy traffic or when towing
- Low transmission fluid
- Sensor or solenoid fault
- Clutch wear in automated manual or dual-clutch gearboxes
What to do
- If it shows overheating, stop safely and let it cool with the engine idling in park, if the handbook advises.
- Avoid aggressive acceleration and heavy loads.
- Have the fault code read; transmission repairs are cheaper if caught early.
Can I keep driving?
Gently, to a safe place or garage, if the car still drives.
MOT
Not a specific MOT item.
Key, immobiliser and security warning lights
A car-and-key or padlock symbol relates to the immobiliser. Why it flashes when parked, and what it means if the car will not start.
A flashing light when parked is usually the alarm or immobiliser showing it is armed. A light at start-up that stays on means the car has not recognised the key.
What it looks like
A car outline with a key or padlock. Colour: Red, green or amber depending on maker.
Common causes
- Flat battery in the key fob
- Using a spare key that is not programmed
- Immobiliser or transponder fault
What to do
- Try the spare key.
- Replace the key fob battery (often a CR2032 coin cell, but check).
- Many keyless cars let you start the car by holding the key against a marked spot on the steering column or start button: see your handbook.
Can I keep driving?
If the car starts and runs, yes.
MOT
No.
Low fuel warning light: how far can you go?
The fuel pump light means you are on reserve. Why the 'miles to empty' figure is only an estimate and the risks of running low, especially on motorways.
The fuel level has reached the reserve, typically several litres.
What it looks like
A fuel pump. Colour: Amber.
Common causes
- Low fuel level
What to do
- Refuel soon. The range estimate is based on recent driving and can drop quickly in traffic or on hills.
- Running out on a motorway is dangerous and can lead to a fine for stopping on the hard shoulder without a valid reason.
- Running a diesel completely dry may mean the fuel system needs bleeding.
Can I keep driving?
Yes, to the nearest fuel station.
MOT
No.
Oil pressure vs oil level warning lights: the difference
Red oil pressure light means stop now; amber oil level means top up soon. How to check and top up your oil safely.
Many cars have two separate oil warnings. Mixing them up can be an expensive mistake.
Oil pressure: red oil can
This means the engine has lost oil pressure. Stop as soon as it is safe and switch off. Running without oil pressure can wreck an engine in minutes.
Oil level: amber, often an oil can with a wavy line or MIN
The oil level is getting low. It is not an emergency, but top up soon with the correct oil grade.
How to check your oil
- Park on level ground and wait a few minutes after switching off (or follow your handbook: some say check warm).
- Pull out the dipstick, wipe it, push it fully back in and pull it out again.
- The level should be between the MIN and MAX marks.
- Some cars have no dipstick and show the level on the dashboard menu instead.
Do not overfill
Too much oil can cause damage too. Add a little at a time and recheck.
Using the right oil
Your handbook lists the specification, such as a viscosity grade (for example 5W-30) and a maker approval code. Using the wrong oil can affect the engine and the DPF on diesels.
If you keep needing to top up
Burning or leaking oil is a sign of wear or a fault. Look for blue exhaust smoke or oil drips, and get it checked.
Power steering warning light
The steering wheel light means power steering assistance has a fault. Steering will feel heavy. What to do and what causes it.
The power steering system has a fault, so assistance may be reduced or lost.
What it looks like
A steering wheel, sometimes with an exclamation mark. Colour: Red or amber.
Common causes
- Electric power steering sensor or motor fault
- Low power steering fluid (hydraulic systems)
- Low battery voltage
What to do
- Steering will still work but may be very heavy, especially at low speed.
- Stop when safe, restart the engine and see if it clears.
- If it stays on, drive carefully to a garage or call for help.
Can I keep driving?
With great care, at low speed, if you can steer safely.
MOT
An electronic power steering warning light is an MOT fail.
Seatbelt reminder light and chime
The red seatbelt symbol and chime remind occupants to belt up. The law, fines, passenger sensors and false alarms.
Someone in a seat with a sensor is not wearing a seatbelt, or something heavy on the seat is being detected as a person.
What it looks like
A seated person wearing a seatbelt. Colour: Red.
Common causes
- Driver or passenger not belted
- Heavy bag on the front passenger seat
- Faulty seat or buckle sensor
What to do
- Make sure everyone is belted. Drivers can be fined up to £500 for not wearing a seatbelt.
- Drivers are responsible for passengers under 14 wearing a belt or the correct child seat.
- Move heavy bags off the seat, or into the footwell.
Can I keep driving?
Yes, once everyone is belted.
MOT
Seatbelts must work correctly to pass; the reminder itself is not a specific item for most cars.
Service due indicator: what the spanner light means
A spanner or 'service due' message is a reminder, not a fault. How service intervals work and how to reset the light.
The car's service schedule (by time, distance or oil condition) says a service is due or nearly due.
What it looks like
A spanner, or a message such as SERVICE DUE or INSP. Colour: Amber or white.
Common causes
- Scheduled service interval reached
- Variable servicing based on oil life
What to do
- Book a service. Keeping a full service history helps resale value and can matter for warranty.
- Independent garages can service a car under warranty if they use approved parts and follow the maker's schedule.
- The reset procedure is in the handbook; garages usually reset it after the service.
Can I keep driving?
Yes.
MOT
No.
The snowflake (frost) warning light
A snowflake on the dashboard warns that the outside temperature is near freezing. What it means for driving and why it is not a fault.
The outside temperature has fallen to around 3–4°C or below, so there may be ice on the road.
What it looks like
A snowflake, usually with a temperature reading. Colour: Amber or white.
Common causes
- Cold weather (it is an information light, not a fault)
What to do
- Expect ice, especially on bridges, shaded roads and untreated side roads.
- Leave much larger gaps: the Highway Code says stopping distances can be up to ten times longer on ice.
- Clear all windows and lights fully before driving.
Can I keep driving?
Yes, with care.
MOT
No.
Traction control and stability control (ESC) lights
A car with skid marks: flashing means the system is working, steady means a fault or that it has been switched off.
Flashing: the system is actively controlling wheelspin or a skid. Steady: the system is switched off or has a fault.
What it looks like
A car with wavy skid lines, sometimes with OFF. Colour: Amber.
Common causes
- Driving on slippery roads (flashing is normal)
- System switched off with a button
- Wheel speed sensor fault (often alongside the ABS light)
What to do
- If flashing, ease off the accelerator and drive more gently.
- If steady, check you have not turned it off.
- If it stays on after restarting, have it checked.
Can I keep driving?
Yes, with care.
MOT
An ESC malfunction warning is an MOT fail.
Tyre pressure (TPMS) warning light
The horseshoe-with-exclamation light means a tyre may be low. How to check, how to reset, and the MOT rule for cars from 2012.
The tyre pressure monitoring system thinks one or more tyres are under-inflated. Flashing then steady usually means a system fault.
What it looks like
A cross-section of a tyre with an exclamation mark. Colour: Amber.
Common causes
- A slow puncture
- Pressure drop in cold weather
- A failed sensor battery (direct systems)
- System not reset after inflating tyres (indirect systems)
What to do
- Check all four tyre pressures when cold against the figures in the door frame or handbook.
- Inflate and follow the handbook to reset the system.
- If one tyre keeps losing air, have it checked for a puncture.
Can I keep driving?
Yes, carefully, to the nearest place you can check pressures, unless a tyre is visibly flat.
MOT
For cars first used from 1 January 2012, a TPMS malfunction is an MOT fail.
Warning light on the motorway: what to do
What to do if a warning light comes on while driving on a UK motorway: amber vs red, emergency areas and when to call 999.
A warning light on a motorway needs a calm plan. The Highway Code and National Highways give clear advice.
Amber light
Keep driving carefully, keep to the left lane and leave at the next junction or services to check the car.
Red light or the car is losing power
- Signal left and move to the hard shoulder, or on a motorway without one, an emergency area (marked with orange surfaces and SOS signs) or the next exit.
- Put your hazard lights on.
- If it is safe, leave the car by the left-hand door and wait behind the safety barrier, well away from traffic.
- Call your breakdown provider. On a motorway with no hard shoulder, you can call National Highways on 0300 123 5000.
If you stop in a live lane
If you cannot get off the carriageway, keep your seatbelt on and hazard lights on, and call 999 immediately. Only get out if you are sure it is safe.
Before you set off
- Fix known warnings before long trips.
- Check fuel, oil, coolant and tyre pressures.
- Keep your breakdown number in your phone.
What warning lights really cost: why acting early is cheaper
Why repair bills for the same warning light vary so widely, what drives the cost, how to get a fair diagnosis and quote, and when an early fix saves money.
"How much will it cost to fix?" is the first question most drivers ask when a warning light comes on. The honest answer is that it depends on the cause, not the light: one engine management warning might be a loose fuel cap, another a failing component. What we can explain is what drives the bill, where early action saves money, and how to make sure you are paying for a real diagnosis. We do not quote prices here, because they vary widely by car, region and garage, and change over time.
Why the same light can mean very different bills?
- One light, many causes. The engine management light covers hundreds of possible faults, from a sensor to an injector.
- Parts prices vary by car. The same part can cost far more for a premium or uncommon model.
- Labour time. A part that is easy to reach on one engine can take hours to get to on another.
- Dealer or independent. Main dealers often charge more per hour but have maker-specific tools; good independents can be better value for older cars.
- Genuine or aftermarket parts. Both can be fine; ask what is being fitted and whether it carries a warranty.
Where ignoring a light gets expensive?
Oil pressure and overheating
These are the big ones. Driving on with low oil pressure or an overheating engine can turn a cheap fix (a top-up, a hose, a thermostat) into a major engine repair. Stop when it is safe.
A flashing engine management light
A severe misfire can send unburnt fuel into the exhaust and damage the catalytic converter, which is usually an expensive part. The original cause may have been a far cheaper ignition component.
Brake warnings
Worn pads left too long can damage the discs, so a pad replacement becomes pads and discs. More importantly, it is a safety risk.
Diesel particulate filter
Acting on a DPF warning early, by following your handbook's advice on regeneration, can avoid a forced clean or replacement.
Tyre pressure
Running on an under-inflated tyre wears it faster, raises fuel or energy use and can damage the tyre beyond repair. A puncture repair is usually far cheaper than a new tyre, if the damage is in the repairable area.
The MOT cost of a warning light
Since 20 May 2018, an illuminated engine management light is a major defect, and the ABS, airbag and stability control warnings also mean a fail. A failed test means a repair and a retest, and a car with a dangerous defect cannot be driven away until it is fixed. Sorting a known warning light before the test avoids that.
How do you get a fair diagnosis and quote?
- Note the details: which light, steady or flashing, when it started, and how the car is behaving.
- Read the code if you can with a basic OBD reader, but do not clear it.
- Ask what the diagnostic fee covers: just reading codes, or testing to find the cause, and whether it is deducted from the repair.
- Ask for a written quote with parts and labour shown separately before work starts.
- Ask to see or keep the old parts. A reputable garage will not mind.
- Get a second quote for large jobs that are not urgent.
- Check the garage: look for reviews and membership of a recognised scheme, and ask about the warranty on the work.
Your rights if a repair goes wrong
Under the Consumer Rights Act 2015, a service must be carried out with reasonable care and skill. If the work was not done properly, you can ask the garage to put it right, and if that is not possible you may be entitled to some money back. Citizens Advice can help with next steps if the garage will not put things right.
Ways to cut the cost without cutting corners
- Do the free checks yourself: oil, coolant (cold), tyre pressures, fuel cap.
- Book amber warnings in promptly, before they cause secondary damage.
- Keep up with servicing: many warnings come from wear items that a service would have caught.
- Check for manufacturer recalls on your vehicle using the free GOV.UK recall checker. Recall repairs are free.
Frequently asked questions
Is a diagnostic check worth paying for?
For anything beyond an obvious cause, yes. Guessing and replacing parts often costs more than a proper diagnosis.
Will my warranty cover it?
If the car is under the manufacturer's warranty or a used-car warranty, check before paying anyone else, as work elsewhere may affect a claim.
Which dashboard warning lights fail an MOT?
Since May 2018 several dashboard warning lights mean an automatic MOT failure in Great Britain. The list, and why.
Since 20 May 2018, the MOT test in England, Scotland and Wales checks several dashboard warning lights. If one of these shows a fault, the car fails.
Lights that cause an MOT failure
- Engine management light (malfunction indicator lamp) staying on.
- Brake system warning lights, including brake fluid and electronic parking brake faults.
- ABS warning light.
- Electronic stability control (ESC) warning light.
- Airbag and seatbelt pretensioner (SRS) warning light.
- Electronic power steering warning light.
- Tyre pressure monitoring system warning on cars first used from 1 January 2012.
- Headlamp levelling or main beam warning lights where fitted and not working.
Bulb checks
The tester also checks that warning lamps light up and go out as designed. Removing a bulb to hide a warning is itself a fail.
Before your MOT
- Start the car and check every warning light goes out.
- Fix faults first. Fault codes can be read by a garage or an OBD-II reader.
- Check exterior lights, tyres, wipers and washer fluid too.
Northern Ireland has its own MOT system with similar checks.
General guidance only; if in doubt, call your breakdown provider.
Frequently asked questions
Why do all the lights come on when I start the car?
That is a self-test. The lights should go out within a few seconds of the engine starting. One that stays on is the one to worry about.
Can I pass an MOT with a warning light on?
Not for the engine management, ABS, airbag or electronic stability control lights, and not for a tyre pressure system fault on cars first used from 2012. The MOT inspection manual lists them.
The light went out on its own. Am I fine?
Possibly. Intermittent faults are common. The fault is usually still stored in the car's memory, so mention it at the next service.
Sources and further reading
- GOV.UK: MOT inspection manual for cars
- GOV.UK: MOT changes from 20 May 2018
- GOV.UK: The Highway Code
- GOV.UK: check MOT history
- GOV.UK: check for vehicle recalls
- National Highways: breakdowns on motorways
- legislation.gov.uk: Consumer Rights Act 2015, section 49
Facts checked on 20 October 2026. Spotted an error? Tell us and we will correct it.