A new light on the dashboard is one of the most common reasons drivers ring a garage, and one of the most misunderstood. Some lights mean pull over now and switch off. Others mean book the car in this week. A few are reminders that can wait. Here is how to read the colours, what the lights you are most likely to see actually mean, what the repair behind each one typically costs in the UK, and where a warranty fits in.
Start with the colour: red, amber and green
Car makers use a simple traffic-light system, and it is the quickest way to judge how serious a warning is before you even know what the symbol means.
| Colour | What it means | What to do |
|---|---|---|
| Red | A safety risk or a fault that can cause serious damage if you keep driving. | Stop as soon as it is safe, switch off and check the handbook. Do not carry on "to get home". |
| Amber or yellow | A fault or a system that needs attention soon. The car is usually safe to drive gently. | Book it in within days, not weeks. If it flashes, treat it as red. |
| Green or blue | Information only: a system is switched on (lights, cruise control, eco mode). | Nothing, unless you did not mean to turn it on. |
Two rules sit on top of the colours. First, a flashing light is more urgent than a steady one. A flashing engine light, for example, usually means a misfire that can destroy the catalytic converter. Second, several lights at once, especially on a modern car, often point to one underlying fault (frequently low battery voltage or a failing alternator) rather than five separate problems.
Symbols vary a little between makes, and newer cars add their own. Your handbook (or the manufacturer's app) is always the final word on what a symbol means on your car.
Red warning lights: stop as soon as it is safe
Oil pressure warning (red oil can)
This is the most expensive light to ignore. It means the engine has lost oil pressure, so the moving parts are no longer properly lubricated. Driving on for even a few minutes can wreck the bearings, the turbo and the timing chain. Stop, switch off and check the oil level when the engine has cooled a little. If the level is fine and the light stays on, have the car recovered rather than driven. The cause can be as cheap as a faulty pressure sensor (around £80–£200) or as serious as a failing oil pump (around £300–£900). If the engine has already been damaged, our guide to engine replacement cost shows where that ends up.
Coolant temperature warning (red thermometer)
The engine is overheating. Keep going and you risk a warped cylinder head and a failed head gasket, which is one of the most common big repair bills in the UK. Pull over, switch off and let the engine cool before you open anything; a hot coolant system is under pressure. Common causes are a coolant leak, a failed water pump, a stuck thermostat or a faulty radiator fan. Our guide to car overheating explains each one, and our water pump and head gasket guides cover the costs.
Battery or charging warning (red battery)
Despite the symbol, this usually means the battery is not being charged, so the car is running on whatever is left in it. That is normally the alternator, its drive belt or the wiring. You may have anything from a few minutes to an hour before the car cuts out, and it often happens with power steering and lights failing first. Turn off non-essential electrics and head somewhere safe. An alternator typically costs £250–£700 fitted; see our alternator replacement cost guide.
Brake system warning (red circle with "!" or "BRAKE")
First check the handbrake is fully off. If it is and the light stays on, the brake fluid may be low or there may be a fault in the hydraulic system. Low fluid often means worn pads or a leak. Do not drive a car whose brake pedal feels soft or sinks.
Power steering warning (red or amber steering wheel)
On most modern cars the steering is electrically assisted. When the system fails, the car still steers but becomes very heavy, which can catch you out at low speed. A red light usually means assistance has gone completely. Repairs range from a software reset to a new steering rack; our power steering repair cost guide has the figures.
Airbag warning (red figure with a circle)
The car is safe to drive in the sense that it will not break down, but the airbags may not deploy in a crash. It is also an MOT failure. Common causes are a worn clockspring in the steering wheel or a connector under a seat.
Amber warning lights: book it in soon
Engine management light (amber engine outline)
The most common amber light, and the least specific. It means the engine computer has stored a fault code, which can be anything from a loose fuel cap to a failing sensor, injector or catalytic converter. Steady means book it in. Flashing means a misfire: reduce speed and get it checked straight away. A diagnostic check usually costs £40–£100. Our full guide to the engine management light goes through the common codes and costs.
Glow plug light (amber coil, diesels only)
On a cold start it should light briefly and go out. If it stays on or flashes while driving, many cars use it to flag an engine fault, often in the fuel, glow plug or emissions system.
DPF warning (amber box with dots)
The diesel particulate filter is filling with soot and needs a regeneration, usually 15–20 minutes at a steady speed on a faster road. Ignore it and the filter can block completely, which is when bills climb. Our DPF guide explains the options, from a forced regeneration to a replacement.
AdBlue warning (amber fluid drop or "AdBlue")
The AdBlue tank is low, or there is a fault in the system that uses it to clean the exhaust. If the tank runs empty, the car will refuse to restart once the countdown reaches zero, so top it up promptly. If the warning returns with a full tank, the cause is usually a sensor, pump or heater; see our guide to AdBlue and EGR problems.
ABS warning (amber "ABS")
Normal braking still works, but the anti-lock system that stops the wheels locking under hard braking does not. The usual cause is a dirty or failed wheel speed sensor, which is often a modest repair (around £80–£250). An ABS pump or control unit is much dearer.
Tyre pressure warning (amber horseshoe with "!")
One or more tyres is low. Check all four with a gauge and inflate them to the figure on the door pillar or fuel flap. If it keeps coming back, you probably have a slow puncture. Some systems need resetting after you correct the pressure.
Traction or stability control (amber car with skid marks)
A brief flash on a slippery road is the system working. A light that stays on means the system has switched itself off, often because of the same wheel speed sensor fault that triggers the ABS light.
Gearbox warning (amber cog, or "limp mode")
On automatics, a gearbox warning often comes with the car stuck in one gear. That is limp mode, designed to get you home without causing more damage. Drive gently and have it diagnosed quickly. Sometimes it is a sensor or low fluid; sometimes it is the mechatronic unit or a clutch pack, which our automatic gearbox guide prices.
Warning lights on hybrid and electric cars
Hybrids and EVs keep most of the familiar lights and add a few of their own. The ones to know are a "check hybrid system" or "EV system" message, a turtle symbol (the car has reduced power to protect the high-voltage battery or motor) and a 12V battery warning. On these cars a weak 12V battery is a very common cause of strange messages, because it powers the computers that start the high-voltage system.
A turtle or a red hybrid system warning should be treated like a red light: drive slowly to somewhere safe and get the car checked. Our guides to hybrid battery health and what goes wrong with electric cars cover the faults behind these messages.
Warning lights and the MOT
Since 2018, several dashboard warnings have been an automatic MOT failure in the UK, including the engine management light, ABS, airbag, electronic stability control, brake fluid, power steering and tyre pressure warnings on cars that have them. A diesel with a DPF warning showing is also likely to struggle on the emissions test. Clearing the code just before the test does not help: the tester checks the system's readiness, and a light that returns on the way home is still a fault. Our list of the most common MOT failures covers the rest.
What warning light repairs typically cost
These are estimated ranges for independent garages in the UK, including parts, labour and VAT. Main dealers usually charge more, and the exact figure depends on the car.
| Light | Common cause | Typical UK cost |
|---|---|---|
| Engine management | Sensor, coil pack, injector, EGR valve | £80–£900 |
| Oil pressure | Pressure sensor or oil pump | £80–£900 |
| Coolant temperature | Thermostat, water pump, radiator fan | £150–£650 |
| Battery / charging | Alternator or drive belt | £120–£700 |
| ABS / traction control | Wheel speed sensor; ABS pump | £80–£1,200 |
| DPF | Forced regeneration; clean; replacement | £100–£1,900 |
| Gearbox / limp mode | Sensor, solenoid, mechatronic unit | £200–£2,500 |
| Power steering | Sensor, motor, steering rack | £150–£1,500 |
The wide ranges are the point. The same light can mean a £90 sensor or a £1,500 repair, which is why a proper diagnosis comes before any guess at the bill.
Does a car warranty pay when a warning light comes on?
A warning light is a symptom, not a claim. What matters is the part that has failed behind it. A mechanical breakdown warranty pays towards eligible repairs when a covered component fails suddenly, such as an alternator, water pump, turbo, oil pump, ABS pump, steering rack or gearbox part. It does not pay for servicing, topping up fluids such as oil, coolant or AdBlue, wear items such as brake pads and tyres, or faults that were already there when cover started. Our guide to what isn't covered by a car warranty explains where those lines usually sit.
Two habits make a claim far more likely to succeed. Stop when a red light tells you to. Damage caused by carrying on after a warning, for example driving with no oil pressure, is commonly excluded. And contact your warranty provider before any repair starts. With ClearPath, the garage must get authorisation before work begins; diagnosis comes first, then the go-ahead.
With ClearPath, eligible claims are covered up to £3,000 per claim, including parts, labour and VAT, with labour up to £100 an hour, a £100 excess and no limit on the number of eligible claims. Cover includes hire car cover up to £45 a day for up to 7 days and recovery up to £60 after a covered breakdown, within the claim limit. Our guide to making a warranty claim walks through the steps.
The bottom line
Read the colour first. Red means stop as soon as it is safe, especially for oil pressure, coolant temperature and charging warnings, because those are the faults that turn a few hundred pounds into a few thousand. Amber means book it in soon, and flashing amber means sooner. Keep the handbook in the glovebox, get a proper diagnosis before you pay for parts, and if the car is out of its manufacturer's warranty, consider cover before the next light appears. To see what cover costs for your car, get an instant quote.
