Dashboard Warning Lights: What They Mean and What to Do

Published 2025-05-31 · By Abed Jabbarkhel, Owner, Park Royal Tyre & Alignment Centre

Dashboard warning lights are your car's way of talking to you, and the colour is the first clue to how worried you should be. This guide explains the traffic-light colour system, walks through the lights that matter most, and shows why a proper diagnostic scan is the only reliable way to turn a glowing symbol into a named fault.

What do dashboard warning light colours mean?

Modern cars follow a traffic-light logic. A red light warns of a serious, potentially dangerous fault, so you should stop as soon as it is safe and get help. Amber or yellow means something needs checking soon but is rarely an emergency. Green, white or blue lights are simply information, telling you a system such as headlights or cruise control is active.

The RAC uses exactly this framework: red means stop and seek a professional, yellow or orange means investigate promptly, and green or blue means the system is working normally Source. If two or more warnings appear together, or a red light is joined by smoke, smell or lost power, treat the situation as urgent whatever the individual colours suggest.

What does the engine management light mean?

The engine management light, also called the EML or malfunction indicator lamp (MIL), is usually an amber engine outline. It means the car's computer has stored a fault in the engine or emissions system. The trigger can be trivial, such as a loose fuel cap or a tired sensor, or serious, such as a misfire, so it should always be scanned rather than ignored.

A steady amber light with normal driving usually means you can continue gently and book a check. A flashing light, or rough running and lost power, points to an active misfire that can wreck the catalytic converter. This light also matters legally: since the May 2018 MOT changes, an illuminated MIL is a specific reason for failure Source.

How urgent are oil pressure and coolant temperature warnings?

These are two of the most urgent lights on any dashboard and both are red for a reason. Low oil pressure, shown by a red oil-can symbol, means vital parts may be running without lubrication. A high coolant temperature warning, or a gauge climbing into the red, means the engine is overheating. Either can cause severe, expensive damage within minutes.

What to do straight away

If the oil light appears, pull over and switch the engine off; the RAC advises stopping as soon as it is safe because the engine can suffer serious damage without proper lubrication. If the temperature warning shows, stop and let the engine cool fully before you even think about opening the coolant cap. In both cases, do not keep driving hoping the light will clear, because by the time it does the damage is often already done.

Why should you never ignore the brake warning light?

The red brake warning light can mean something as harmless as the handbrake being left on, or something as serious as low brake fluid, worn pads triggering a sensor, or a hydraulic fault. Because braking is safety-critical, this is one light you should never leave until your next service.

First, check the handbrake is fully released. If the light stays on, keep your speed low, avoid harsh braking and get the brakes and fluid inspected quickly. A separate amber brake-pad wear light simply means pads are near the end of their life and should be replaced soon. Any persistent red brake warning deserves the same caution as an oil or temperature light.

What does the battery or charging light mean?

A red battery-shaped symbol rarely means the battery itself has died. It usually signals that the charging system is not keeping up, most often because of a failing alternator, a slipping or broken drive belt, or worn wiring. The car is then running on stored charge that will eventually run flat, sometimes leaving you stranded without power steering or lights.

If this light stays on while driving, switch off non-essential electrics such as heated screens and the stereo, and head somewhere it can be checked before the battery drains. A charging-system test quickly shows whether the alternator, belt or battery is at fault. Our workshop can test all three together so you replace only the part that has actually failed, not the whole lot on guesswork.

Will an ABS or airbag light fail your MOT?

Yes, in most cases. Since the MOT rules were updated in May 2018, testers must check dashboard warning lamps, and an illuminated light that shows a genuine malfunction counts as a major defect and a fail. This applies to the ABS, airbag (SRS) and engine management lights among others, so a car cannot simply be nursed through its test with a warning glowing.

The official MOT inspection manual states that an SRS malfunction indicator lamp illuminated to show a fault is a failure, though a lamp merely showing a disabled passenger airbag is not Source. The ABS warning lamp is covered under lamps and electrical equipment, where an illuminated light indicating a malfunction is also a reason for rejection Source.

Practically, an ABS light usually means ordinary braking still works but the anti-lock function may not, so stopping distances can lengthen on wet or loose surfaces. An airbag light means the restraint system might not deploy in a crash. Neither should be left unresolved, both for safety and to avoid a wasted MOT attempt.

What about TPMS, DPF and power steering lights?

These three amber lights are common and often misunderstood. The tyre pressure monitoring system (TPMS) light warns that one or more tyres are low, the diesel particulate filter (DPF) light flags a clogging filter, and the power steering light signals a fault in the steering assistance. Each needs prompt attention, though none is usually an instant roadside emergency.

• TPMS light: check and correct all tyre pressures, then look for a slow puncture. On cars first used from 1 January 2012, a faulty TPMS is an MOT failure.
• DPF light: often clears after a longer, faster drive that lets the filter regenerate; if it stays on, get it checked before a costly forced regeneration or replacement is needed.
• Power steering light: the steering may suddenly feel heavy. Reduce speed and have it diagnosed, as many systems disable assistance when a fault is detected.

Why does a diagnostic scan find the real fault?

A warning light only tells you a system has flagged a problem, not what that problem is. Behind the light, the car's computer stores fault codes that pinpoint the affected circuit or component. Reading those codes with proper equipment turns a vague amber glow into a specific answer, so you fix the actual cause instead of replacing parts by trial and error.

This matters most with the engine management light, where a dozen very different faults share one symbol. Our diagnostic equipment reads the stored and pending codes, live sensor data and freeze-frame information to show what triggered the light and when. It also reveals intermittent faults that have logged a code even after the light has gone out, catching problems early before they leave you stranded.

When should you stop immediately versus book in?

The simple rule is to stop as soon as it is safe for any red light, and especially for oil pressure, coolant temperature or brake warnings. For most steady amber lights the car can usually be driven carefully and booked in within a few days for a scan, so long as it feels and sounds normal.

Override that rule the moment other symptoms appear. Smoke, a burning or fuel smell, loss of power, warning buzzers or unusual noises mean you should stop and call for advice regardless of colour. Drivers around Park Royal and West London can reach our NW10 workshop quickly, and if the car is not safe to move, it is safer to arrange recovery to our workshop than to risk further damage by driving on.

Frequently asked questions

Is it safe to drive with the engine management light on?

If the light is steady amber and the car drives normally, you can usually drive gently and book a diagnostic check. If it is flashing, or the car is misfiring, juddering or losing power, slow down and get it checked quickly, as continuing risks expensive damage to the catalytic converter.

Will a warning light fail my MOT?

Often, yes. Since May 2018 MOT testers check dashboard warning lamps, and an illuminated airbag, ABS or engine management light that shows a genuine malfunction is a major defect and an automatic fail. It is far cheaper to diagnose and fix the fault before the test than to pay for a retest.

Why did a warning light come on and then go off?

An intermittent light usually points to an early or occasional fault that the computer has logged as a code. Even after the light clears, that code is normally still stored, so a diagnostic scan can reveal what triggered it and let you act before it becomes a recurring or worsening problem.

Can you tell me what a light means over the phone?

We can often give initial guidance if you describe the colour, the symbol and how the car is behaving. For anything red or safety-related, though, the safe advice is to stop and have it checked properly rather than guess, since the same symbol can hide very different faults.

How much does a diagnostic check cost and how long does it take?

Costs vary with the make and the complexity of the fault, so it is best to call for a quote. A basic code read is quick, often taking minutes, while tracing an intermittent or multi-system fault takes longer. As an RAC and AA approved garage, we will always explain what we find before doing any work.

Seeing a warning light you are unsure about? Do not guess. Call Park Royal Tyre & Alignment Centre on 020 3886 2355, message us on WhatsApp at 07476 586 589, or book a diagnostic check at our Park Royal workshop. We will read the fault codes and tell you exactly what is going on.