Car Warning Light Symbols: What Your Dashboard Is Telling You

Modern cars can throw dozens of symbols at you, and most drivers know maybe six of them. The good news is that you do not need to memorise every icon, because the colour tells you almost everything you need to know about urgency, and the handbook covers the rest.

This guide works through the colour system first, then the individual lights that matter most, what actually causes each one, and what to do about it.

What do the colours of car warning lights mean?

Every manufacturer uses the same broad colour code, which is set out in international standards and does not vary much between makes.

Two extra rules on top of the colours:

• Flashing beats steady. A flashing light means the fault is happening right now and is likely causing damage, rather than having been logged at some point.
• A light that comes on while you are moving is more serious than one that never went out at start up. All warning lights illuminate briefly when you turn the ignition on, as a bulb check. If one stays on after the engine starts, the system has failed its self test. If one appears halfway through a journey, something has just gone wrong.

Which warning lights mean stop driving immediately?

Stop as soon as you can do so safely if you see any of these:

• Red oil pressure light. Continuing to drive can wreck the engine within a minute or two.
• Red coolant temperature light or a temperature gauge in the red. Overheating warps cylinder heads and blows head gaskets.
• Red brake system light with the handbrake released.
• Red battery or charging light, because you are running on battery alone and will lose power steering and brakes assistance when it goes flat.
• Flashing engine management light.
• Any red light accompanied by a change in how the car drives, sounds or smells.

Pull over somewhere safe, off the carriageway if you can. On a motorway use the hard shoulder or an emergency area, get out on the passenger side and stand behind the barrier. Then decide whether to call for recovery rather than trying to nurse the car home.

Engine management light (check engine light)

The engine management light, also called the malfunction indicator lamp or check engine light, is an amber engine outline. It means the engine control unit has detected something outside its expected parameters and stored a fault code.

It is deliberately vague, because it covers the entire engine and emissions system. Common causes, roughly in order of how often we see them:

• A loose, damaged or missing fuel filler cap, which lets the evaporative emissions system fail its pressure test.
• A failing oxygen (lambda) sensor.
• A mass airflow sensor contaminated with oil from an over oiled performance air filter.
• Ignition coil or spark plug failure causing a misfire.
• A split or perished vacuum or induction hose.
• EGR valve sticking with carbon build up, very common on diesels used for short journeys.
• A blocked diesel particulate filter or a failing catalytic converter.

Steady light versus flashing light

A steady amber light means drive gently and get the code read within a few days. Avoid heavy acceleration and towing.

A flashing light means a live misfire. Unburnt fuel is being pushed into the exhaust, where it burns in the catalytic converter and can melt the substrate. Reduce speed, avoid load, and stop as soon as you safely can. A replacement catalytic converter costs many times more than the coil pack that caused the problem.

What to do

Check the fuel filler cap first, because it takes ten seconds and is a genuinely common cause. Turn the engine off and back on to see whether the light clears after a few journeys. If it does not, get the fault code read. Most garages and many parts shops read codes for a small fee or free, and a code reader is inexpensive if you want your own.

Battery and charging system warning light

The red battery symbol does not mean the battery is flat. It means the charging system is not putting current back in, so the car is running on stored battery power alone.

Usual causes:

• A failed or failing alternator.
• A broken, slipping or shredded auxiliary drive belt, which on most cars also drives the water pump and power steering pump.
• Corroded or loose battery terminals or a poor earth strap.
• A failed voltage regulator.

What to do

Turn off everything you do not need: heated rear screen, heated seats, air conditioning, radio, and headlights if it is daylight and safe. Head for the nearest garage or home, whichever is closer, and be aware that when the battery runs down the engine will stop and you may lose power steering assistance and brake servo assistance.

If the light came on alongside a squealing noise, a rising temperature gauge or heavy steering, the drive belt has probably gone. In that case stop straight away, because with no water pump the engine will overheat very quickly.

Oil pressure warning light

The red oil can symbol means oil pressure has dropped below the safe minimum. This is the single most damaging light to ignore, because an engine running without oil pressure can seize in under a minute.

Do not confuse it with the amber low oil level light that some cars have. Low level is a warning to top up at your convenience. Low pressure is a stop now warning.

Common causes:

• Genuinely low oil level, often through consumption on an older engine.
• A failing oil pump or a blocked pick up strainer.
• A clogged oil filter on an overdue service.
• Oil that has been thinned by fuel dilution from repeated short cold journeys.
• A faulty oil pressure sensor, which is the best case scenario but should never be the assumption.

What to do

• Pull over immediately and switch off the engine. Do not drive on to somewhere more convenient.
• Wait a few minutes, then check the level on the dipstick with the car on level ground.
• If it is low, top up with the correct grade and restart. If the light goes out and stays out, drive gently and find out where the oil went.
• If the light stays on with a correct oil level, do not drive. Call for recovery.

Coolant temperature warning light

The red thermometer in wavy lines means the engine is overheating. Some cars also show a blue version of the same symbol at start up, which simply means the engine is still cold and is not a fault.

Causes include a coolant leak from a hose, radiator or water pump, a failed thermostat stuck closed, a broken drive belt driving the water pump, a blocked radiator, a failed cooling fan, or a head gasket failure pushing combustion gases into the coolant.

What to do

• Pull over, switch the engine off and open the bonnet to let heat escape. Do not stand over it.
• Never open the expansion tank cap on a hot engine. The system is pressurised and the coolant is above boiling point. Wait until it is cool enough to hold your hand on the top hose.
• Once cool, check the coolant level in the expansion tank and look underneath for drips and for steam.
• Top up with the correct coolant mixture for your car, not plain water. Coolant is an antifreeze and a corrosion inhibitor as well as a heat transfer fluid, and modern engines with aluminium heads corrode quickly on water alone. Plain water is an emergency measure only, to be drained and replaced properly afterwards.
• If it overheats again, or if the coolant looks like coffee or has oil in it, stop and get it recovered.

Brake system warning light

The red circle containing an exclamation mark comes on whenever the handbrake is applied, which is normal. If it stays on with the handbrake fully released, there is a fault.

Causes:

• Low brake fluid, which almost always means either a leak or brake pads that have worn far enough to draw fluid down into the calipers.
• A failed brake fluid level sensor.
• A fault in the hydraulic system or, on some cars, a brake pressure or servo fault.
• On cars with an electronic parking brake, a fault in the parking brake actuator.

What to do

Check the handbrake is fully off first. Then check the brake fluid level against the minimum and maximum marks on the reservoir. If it is at or below minimum, do not drive: a hydraulic leak can take the brakes away entirely with no further warning. If the pedal feels soft, spongy or long, stop regardless of what the fluid level says.

If the level is correct and the pedal feels normal, it may be a sensor, but it still needs diagnosing quickly. It is also an MOT failure.

ABS warning light

The amber circle with ABS inside means the anti lock braking system has taken itself offline. Your normal brakes still work. What you lose is the ability to brake hard without locking the wheels, and with it your ability to steer during emergency braking.

The usual cause is a wheel speed sensor, either failed, unplugged, or with a damaged reluctor ring. Sensor wiring runs down inside the wheel arch where it gets salted, stone chipped and pulled about, so failures are common on older cars and on cars that have been through kerb impacts. Low brake fluid, a failed ABS pump or module, and a flat battery event can also trigger it.

Because ABS and the stability control system share wheel speed sensors, an ABS fault often brings on the traction control or ESP light at the same time.

What to do

Drive gently, leave a much bigger gap, and be aware that in an emergency stop the wheels can lock. Avoid heavy braking in the wet. Get it read as soon as possible, both because it is a safety system and because it fails the MOT.

Airbag and SRS warning light

The airbag light shows a seated figure with an inflated bag in front of them, or the letters SRS. When it stays on, the supplementary restraint system has faulted and the airbags may not deploy in a collision. Seat belt pretensioners are part of the same system, so they may not fire either.

Common causes:

• Corrosion or a poor connection in the connector under a front seat, disturbed by sliding the seat back and forth or by a spilt drink.
• The clock spring in the steering column wearing out, which often also kills the horn and the steering wheel controls.
• A crash sensor or wiring damaged in a previous impact, including a low speed knock to a bumper or door.
• A previously deployed airbag or pretensioner that was not properly replaced.
• Water ingress into a control module mounted low in the car.

What to do

Do not ignore it and do not simply clear the code. Airbag systems store crash data and lock themselves out after certain events for a reason. Have it read on equipment that can talk to the SRS module, which not every basic code reader can do.

If the light appeared after any kind of collision, however minor, get the whole restraint system checked as part of the repair. Signature carries out vehicle body repairs on everything from car park knocks to accident damage, and part of any proper post impact repair is confirming that the safety systems behind the panels are intact rather than just making the outside look right.

Tyre pressure monitoring system (TPMS) light

The amber symbol looks like a cross section of a tyre with an exclamation mark inside it. It means at least one tyre has lost pressure, or that the monitoring system itself has faulted.

There are two types of system. Direct TPMS uses a battery powered sensor inside each wheel that transmits actual pressure. Indirect TPMS works out that a tyre is soft by comparing wheel speeds through the ABS sensors, because an underinflated tyre has a smaller rolling radius and turns faster.

Causes:

• A genuine pressure loss, including the slow seasonal drop that happens as the weather gets colder.
• A puncture, which may be slow enough that the tyre still looks normal.
• A corroded or leaking valve, common where alloy wheels and aluminium valve stems have been exposed to road salt.
• A damaged or buckled rim, which lets air past the tyre bead. In the UK this is usually a pothole or kerb impact.
• A flat sensor battery, typically after five to ten years, or a sensor not paired after a wheel change.
• The system not being reset after inflating the tyres, on cars that require a manual reset.

What to do

Check all four pressures cold against the placard on the driver's door shut, the fuel filler flap or the handbook, and inflate them to spec. Reset the system if your car needs it. If the light returns within a week or two, there is a leak somewhere.

If the tyre keeps deflating and no puncture can be found, the wheel itself is a likely culprit. Kerb and pothole damage that cracks or distorts a rim is common on Greater Manchester roads, and a wheel that will not seal is a safety issue as well as an annoyance. Our alloy wheel repair service covers straightening and refinishing kerbed and damaged wheels, mobile at your home or workplace.

Power steering warning light

Usually a steering wheel outline with an exclamation mark, in amber or red depending on the make. On cars with electric power steering, this means the assistance has reduced or shut down. The steering still works, but it becomes very heavy, particularly at parking speeds.

Causes on electric systems include a failed steering torque sensor, a fault in the steering rack motor, low battery voltage, or a related fault elsewhere on the network. On older cars with hydraulic power steering, the causes are low fluid, a leaking pipe or rack, a slipping belt or a failing pump.

What to do

If the car has hydraulic steering, check the fluid level and look for leaks. If it is electric, there is nothing to check under the bonnet. Either way, drive slowly and be ready for heavy steering, especially when manoeuvring. It is an MOT failure and needs diagnosing.

Diesel particulate filter (DPF) light

An amber box containing dots or a filter symbol, found on diesels. It means soot has built up in the particulate filter and the car needs to regenerate it, or the filter is already blocked.

DPFs clean themselves by burning off soot at high exhaust temperatures, which requires a sustained run at reasonable speed. A diesel used only for short urban journeys never gets hot enough, so the soot accumulates.

What to do

When the light first appears, and if the handbook agrees, take the car for a continuous run of 20 minutes or so at a steady speed on a dual carriageway in a lower gear than normal, keeping the revs up. That usually triggers a regeneration and the light goes out.

Do not ignore it. Once the DPF light is joined by the engine management light and the car drops into limp mode, the filter needs forced regeneration or cleaning by a garage, and a replacement filter is a genuinely expensive part. If your driving is nearly all short journeys, a diesel is the wrong car for you.

Other lights you will see

Which warning lights fail the MOT?

Since the MOT changes in 2018, several illuminated warning lamps are recorded as major defects and fail the test outright:

• Engine management light (malfunction indicator lamp)
• Airbag and SRS warning light
• ABS warning light
• Brake system or brake fluid warning light
• Electronic power steering warning light
• Electronic parking brake warning light
• Stability control warning light on vehicles first used from January 2012
• Tyre pressure monitoring light on vehicles first used from January 2012

The tester also checks that the lamps themselves work, so removing a bulb or taping over a light fails as well. Clearing a code before the test only helps if the fault is genuinely fixed, because most systems re illuminate the lamp within a drive cycle or two.

How to read a fault code yourself

Every petrol car sold in the UK from 2001 and every diesel from 2004 has a standard EOBD diagnostic socket, usually within reach of the driver's footwell or behind a panel below the steering column.

A basic code reader or a Bluetooth dongle paired to a phone app will pull the stored codes and give you a description. That tells you the area of the fault, which is genuinely useful, but understand the limits:

• A code names the circuit that reported a problem, not the part that failed. A code pointing at an oxygen sensor can be caused by an exhaust leak upstream of it.
• Cheap readers often only see generic engine codes and cannot access the airbag, ABS or body modules.
• Clearing codes without fixing anything wipes the freeze frame data that a technician would have used to diagnose it.

Read the code, note it down, then decide whether it is something you can address or something for a garage.

How to keep warning lights off in the first place

Most avoidable warning lights come down to routine maintenance and driving pattern.

• Service the car on schedule, using the correct oil specification rather than whatever is cheapest.
• Check oil and coolant levels monthly, and before any long trip.
• Check tyre pressures monthly when the tyres are cold, and after significant temperature changes.
• Replace air and fuel filters at the recommended intervals.
• Give a diesel a proper run at sustained speed regularly, so the DPF can regenerate.
• Keep battery terminals clean and tight, and replace a battery that is struggling rather than waiting for it to fail. Low voltage causes a surprising number of unrelated warning lights on modern cars.
• Deal with small faults promptly. Most expensive repairs started as an amber light that was ignored for a month.

Finally, keep the handbook in the car. Manufacturers use variations on the standard symbols, and the handbook section on warning lights is the definitive answer for your specific model.