Dashboard Warning Lights Explained: What Every Symbol Means, and Which Ones Mean Stop Now

A woman rang me last winter from a lay-by on the Dudley bypass. Red light on the dash, engine still running, no idea whether to carry on the last two miles home or wait for me. She'd been sat there twenty minutes.

It was the oil pressure light. She'd made the right call, and it probably saved her engine.

The problem is that almost nobody is taught what these things mean. You get a symbol, no words, and a decision to make in about four seconds. So here's the plain version: every light that matters, what it's actually telling you, and whether you can keep driving.

Dashboard warning lights follow a traffic light system. Red means stop as soon as it is safe to do so, because carrying on risks serious damage or your safety. Amber or yellow means a fault has been detected and needs looking at soon, but you are not usually in immediate danger. Green and blue are information only, telling you a system is switched on.

If you remember nothing else, remember that. Red, pull over. Amber, book it in. Green, ignore it.

There is one exception, and it's an important one. A flashing amber light is treated as a red. More on that further down.

Oil pressure warning (red oil can)

This is the one that ends engines. It does not mean you're low on oil, it means the oil is not being pushed round the engine at the right pressure. Without that, metal runs on metal, and you can destroy an engine in under a minute.

Can you keep driving? No. Pull over safely, switch the engine off, and check the oil level once it's cooled. If the level is fine and the light still comes on, do not restart it. That's a recovery job, not a drive-home job. If you're not sure how often yours should be changed, we've covered when to change your engine oil separately.

Engine temperature (red thermometer, or a red thermometer in water)

Your engine is overheating. Usually a coolant leak, a failed thermostat, a duff water pump or a broken cooling fan.

Can you keep driving? No. Overheating warps cylinder heads and blows head gaskets, and that's a four-figure repair on most cars. Pull over, switch off, and let it cool for at least half an hour before you even think about opening the bonnet. Never take the cap off a hot cooling system.

Battery and charging (red battery symbol)

Here's the bit that catches people out: this light is almost never about the battery. It means the charging system has stopped charging, and nine times out of ten that's the alternator or the belt driving it.

Can you keep driving? Only briefly. The car is now running purely off whatever charge is left in the battery, so you've got a short window before everything shuts down. Turn off the stereo, heated seats, air-con and anything else you don't need, and head straight home or to a garage. Do not switch the engine off unless you're happy where you've stopped, because it may not restart. If your battery has been struggling generally, the seven signs a battery is dying is worth a read.

Brake system warning (red circle with an exclamation mark, or the word BRAKE)

Three possible causes. The handbrake is still on, the brake fluid is low, or there's a fault in the braking system.

Can you keep driving? Check the handbrake first, because that's the answer more often than you'd think. If it's off and the light stays on, stop. Low brake fluid usually means worn pads or a leak, and a leak means you can lose braking entirely. If the pedal feels soft or is going further than usual, that's a recovery job. We've covered the warning signs your brakes need attention in more detail.

Airbag / SRS (red person with a circle in front of them)

A fault in the airbag or seatbelt pretensioner system. The car drives perfectly normally, which is exactly why people ignore it for years.

Can you keep driving? Mechanically, yes. But your airbags may not deploy in a crash, and they may also deploy when they shouldn't. It's also a straight MOT failure. Our diagnostic equipment reads the airbag system, so it's a quick one to get answered.

Power steering (red steering wheel, sometimes amber with an exclamation mark)

The electric or hydraulic power assistance has faulted.

Can you keep driving? Carefully, and not far. The steering still works, but it'll go very heavy, especially at low speed and when parking. If it fails suddenly at speed it's alarming. Also an MOT failure on most cars built after 2012.

Engine management light (amber engine outline)

Also called the check engine light, EML or MIL. The single most common light I get called about, and the most misunderstood.

It means the engine's computer has logged a fault somewhere in the engine or emissions system. That covers everything from a loose fuel cap to a failing turbo. The light itself tells you nothing about severity, which is why guessing is pointless.

Can you keep driving? If it's steady and the car feels normal, yes, but get it read within a week or so. Our car diagnostics covers exactly this. If it's flashing, see below.

Diesel particulate filter (amber box with dots in it)

Diesel only. The filter that catches soot from your exhaust is clogging up. It's usually caused by lots of short, cold, stop-start journeys, which is most Black Country driving.

Can you keep driving? Yes, and in fact driving is the fix. Get it out on a dual carriageway for twenty minutes at a steady 2,000rpm or more, in a lower gear than normal, and it should burn itself clean. Ignore it for weeks and you'll go into limp mode and end up needing a forced regeneration or a new filter, which is a genuinely expensive job. If it keeps coming back, something else is causing it and it needs proper fault finding rather than another motorway run.

ABS (amber letters ABS in a circle)

The anti-lock braking system has faulted. Usually a wheel speed sensor, which is a common and reasonably cheap fix.

Can you keep driving? Yes. Your normal brakes still work exactly as they did. What you lose is the anti-lock function in an emergency stop, so leave more room and get it sorted. It's an MOT failure.

Traction control / ESP (car with wavy lines behind it)

If it flashes briefly while you're driving, that's normal, it means the system is working and you've found a slippery patch. If it stays on solid, the system has a fault, and it very often shares a sensor with the ABS.

Can you keep driving? Yes, but with less help if you lose grip. Electronic stability control faults are an MOT failure.

Tyre pressure monitoring (amber horseshoe with an exclamation mark)

One or more tyres is low, or a sensor has failed. The sensors have batteries in them and they do just die of old age, usually around seven to ten years.

Can you keep driving? Check your pressures at the next petrol station and reset the system. If they're all correct and the light stays on, it's a sensor. Worth sorting before an MOT.

Glow plug (amber coil, like a spring on its side)

Diesel only. If it comes on when you turn the key and goes out after a few seconds, that's completely normal, it's preheating the cylinders. If it stays on or flashes while you're driving, that's a fault.

Can you keep driving? Yes, but expect hard starting on cold mornings. A flashing glow plug light on some cars is also used as a general engine fault warning, so get it read.

AdBlue (amber canister, or the word AdBlue)

Modern diesel only. Your AdBlue tank is running low. The car will warn you, then restrict performance, then refuse to start at all once it's empty.

Can you keep driving? Yes, but top it up. You can buy it at any petrol station or motor factor. Do not let it run to zero, because getting the system to reset afterwards can need a garage.

Service or spanner light (amber spanner)

Not a fault. It's a mileage or time reminder telling you a service is due.

Can you keep driving? Yes. But book it in, because a service is the cheapest thing you'll do for your car all year. Our car servicing starts from £99 and a full service is £149, and if you want the detail, here's what a service actually includes.

Green and blue symbols are telling you something is switched on, not that something is wrong. Main beam (blue), side lights, indicators, cruise control, eco mode, that sort of thing. Nothing to do. If a green light is flashing quickly on your indicators, you've usually got a blown bulb, and that's an MOT fail for the sake of a few quid.

Because the ECU has stored a fault code. The most common causes I see, roughly in order:

• ▸A faulty or dirty mass airflow sensor
• ▸A failed oxygen or lambda sensor
• ▸An EGR valve stuck or clogged with carbon
• ▸A misfire from worn spark plugs or a failing coil pack
• ▸A boost or vacuum leak, often a split pipe
• ▸A DPF or emissions fault on diesels
• ▸A loose or perished fuel cap, which really does do it

Notice the spread. The cheapest of those is a fuel cap. The dearest can run into four figures. There is no way to tell them apart by looking at the light, and no way to tell by driving it. It has to be read.

If the light is steady and the car drives normally, with no loss of power, no odd noises and no smoke, it's generally safe to drive short distances for a few days while you get it booked in.

If any of the following are true, stop driving it:

• ▸The light is flashing
• ▸The car has gone into limp mode, so it won't rev past about 3,000rpm or is stuck in third gear
• ▸You've lost noticeable power
• ▸There's smoke, a smell of fuel, or a new noise
• ▸The temperature or oil light has come on as well

A flashing engine management light means an active misfire. Unburnt fuel is being dumped into your exhaust, and that fuel burns inside the catalytic converter instead of the engine.

That destroys the cat, and cats are expensive. On some cars you can do it in a matter of minutes.

Treat a flashing engine light as a red light. Pull over, switch off, and call someone. Driving it home "because it's only ten minutes" is how a coil pack becomes a coil pack plus a catalytic converter.

Since the MOT rules changed in 2018, testers check warning lamps as part of the test. If one of these is lit and showing an active fault when you turn up, it's a fail:

• ▸Engine management light (MIL)
• ▸ABS
• ▸Airbag / SRS
• ▸Brake system warning
• ▸Electronic stability control
• ▸Power steering, on cars fitted with it
• ▸Tyre pressure monitoring, on cars fitted with it

Service reminders, low fuel and low screenwash don't affect the test.

This catches a lot of people out, because the car drives perfectly well with an airbag light on and they've stopped noticing it. Then it fails, they pay for the diagnosis and the repair anyway, and they've lost the test fee on top. Check your dashboard a fortnight before your MOT is due, not the night before. Our full pre-MOT checklist covers the rest of it, and here's what an MOT actually costs.

You can, and plenty of places will do it. It's worth understanding what you're getting.

A free code read gives you a code. Something like P0171. That tells you the ECU noticed the engine was running lean. It does not tell you whether that's a split vacuum pipe worth a fiver, a dirty airflow sensor, a failing lambda sensor or an injector problem. The code is the symptom, not the diagnosis.

I've lost count of the cars I've seen where someone read a code, bought the part the internet said matched it, fitted it, and the light came straight back on. They're now down the cost of the part and no further forward.

Proper diagnosis means reading the codes, then reading live data from the sensors while the engine runs, then testing the actual component before anyone spends money on it. That's what a full diagnostic check is, and it's why you get a written report at the end rather than a number scribbled on a receipt.

Our car diagnostics starts from £45. That covers plugging in, reading the stored and pending codes, checking live data, and telling you what's actually wrong and what it'll cost to fix. You get a written report with the codes, what they mean in plain English, and a parts and labour estimate.

You get a price before any work happens. If it turns out to be something I can sort in five minutes while I'm there, I'll tell you that too.

And because I'm mobile, I come to you, so the car doesn't need to be driven anywhere with a warning light on. That matters more than people realise when the light is a red one.

The worst thing you can do with a warning light is have someone clear it without finding out why it was on.

It'll go off. It'll feel fixed. It will come back, usually at the least convenient moment, and in the meantime whatever caused it has had a few more weeks to do damage. I won't clear a code without diagnosing it first, and if a garage offers to just reset it for you, that should tell you something.

The second worst thing is ignoring an amber light for six months because the car "seems fine". Amber lights are the cheap stage. Red lights are the expensive stage. The whole point of the amber one is that you've been given time.

Got a light on and no idea what it is? Send me a photo of the dashboard on WhatsApp and I'll tell you straight whether it can wait. If it can, I'll say so. We cover everywhere from Dudley and Stourbridge to Halesowen and Brierley Hill.