What Red and Amber Warning Lights Actually Mean (and Which Fail an MOT)

• A red dashboard warning light means stop when it is safe and call for help. An amber light means get the car checked soon. Green and blue lights show a system is working.
• Some amber lights fail an MOT: the GOV.UK MOT inspection manual lists the ABS lamp, the airbag lamp, the electronic stability control lamp and the engine malfunction lamp as Major defects.
• The same colour does not always mean the same urgency. A solid amber ABS light usually lets you drive on with care, while an ABS light that appears with the red brake light means stop.

What Red and Amber Warning Lights Actually Mean (and Which Fail an MOT)

The colour tells you how fast to act. Red means a serious fault and the RAC’s advice is to stop driving as soon as it is safe and call for recovery. Amber means a fault that needs attention soon, and the RAC says to have the vehicle checked by a mechanic as soon as possible. Green, white and blue lights are information only. The AA puts the red rule in one line: “Red warning lights mean you need to take immediate action.”

That rule of thumb covers most cases, but a few lights break the pattern, and four amber lights can fail the car at its next MOT. This guide explains the colours, the lights that need the most care, and what the MOT inspection manual says.

The Colour Code: Red, Amber, Green and Blue

Red is the warning for a fault that can cause damage or danger within minutes. Typical examples are low oil pressure, an overheating engine, a brake system fault, a charging fault and a faulty airbag system. What Car describes red as “a serious problem” that needs immediate attention, and advises drivers to stop as soon as it is safe and seek advice.

Amber (some cars show it as yellow) means a system has detected a fault but the car is usually safe to drive for a short distance. What Car says amber lights show something will soon need attention. Typical examples are the engine management light, ABS, tyre pressure, the diesel particulate filter and brake pad wear. An amber light is not an emergency, but it is also not a light to leave for months.

Green and white lights show a system is active, such as indicators, cruise control or auto start-stop. Blue usually means the main beam headlights are on. What Car adds that some cars use blue to show the engine has not yet reached operating temperature.

The Red Lights That Need the Most Care

Oil pressure. The RAC says this light comes on when oil temperature is too high or the oil level or pressure is too low, and advises stopping as soon as it is safe and switching off the engine. If the dipstick shows the level is fine, call for recovery, as driving further could damage the engine. The AA says that if the light stays on after topping up, switch off the engine and call for help.

Battery and charging. The RAC says you should not drive with the battery warning light on, as the car can suffer a sudden power failure. The AA advises pulling over safely and switching off the engine, and not restarting it, as that could make the fault worse.

Brake system. What Car notes the red brake light can just mean the handbrake is still partly on. If the handbrake is fully released and the light stays on, the AA says that where the pedal needs more pressure than usual, you should pull over and get help. If the brake light appears together with the ABS light, the AA says do not drive: stop and call for help. The RAC gives the same instruction.

Engine temperature. The RAC says to stop straight away to avoid irreparable engine damage. The AA says to pull over, check the coolant level and, if the light comes back after topping up, get the car checked. What Car warns never to open the radiator cap while the engine is hot.

Airbag. The RAC says you should not drive with a red airbag warning light on, and the AA says it is not safe to ignore. What Car points out that the airbags might not deploy in a crash if the light is on, and that this light can be red or amber depending on the car.

The Amber Lights Worth Knowing

Engine management. A solid amber light usually means a lesser fault, and a flashing light is more serious. The AA advises that if the light stays on with no loss of power, get it checked as soon as possible. If it flashes, avoid heavy acceleration, stop safely and restart after two minutes, and if it keeps flashing, switch off the engine and call for help.

ABS. The RAC says that if the ABS light comes on alone, it is safe to continue your trip. The AA says driving is usually fine with care, especially in wet or icy conditions, and the fault should be checked soon. The normal brakes still work, but What Car notes that stopping distances in an emergency can increase.

Tyre pressure. What Car says to check and inflate the tyres, reset the system, and look for a puncture if the light returns. Tyre pressure monitoring has been a UK requirement on new cars sold from November 2014. The AA says it is acceptable to complete your trip or reach a garage, while the RAC advises stopping when it is safe to check the pressures. The safest course is to check the pressures at the next safe stop.

Diesel particulate filter. The AA says the DPF light is often safe to drive with, and that driving for about 10 minutes above 40mph can clear it. If the light stays on, get help. The RAC advises a garage visit as soon as you can, as driving with a blocked filter could cause more serious damage.

Brake pad wear. The AA lists worn brake pads as not safe to drive on and says to get replacements soon. What Car treats it as less urgent, saying the pads are nearing the end of their life and replacements should be booked soon. Either way, do not leave it.

Which Warning Lights Fail an MOT

The MOT inspection manual on GOV.UK sets the rules testers use. Its Major category is a defect that counts as a fail. Under section 1 on brakes, an ABS warning device that is not working, or that shows a system malfunction, is listed as Major. Under section 7 on other equipment, an SRS airbag malfunction lamp indicating a system malfunction is Major, and so is an electronic stability control lamp indicating a malfunction. The manual tells testers to fail only if they are certain the lamp indicates a fault. Under section 8, an engine malfunction indicator lamp that is inoperative or indicating a malfunction is Major on the petrol and diesel emissions tests.

The manual lists a brake fluid warning light that is illuminated or defective as Minor, which means it is recorded but not a fail on its own. Blackcircles says the tyre pressure light will not fail an MOT, but it warns the light can hide a real pressure problem. That site also says a diesel particulate filter light that stays on is a fail, which is a reason to treat a stuck DPF light seriously. A lit lamp showing the passenger airbag has been switched off is not a defect, according to the manual.

In practice, if one of the four main amber lights is on at test time, expect the garage to fail the car and plan for the repair first.

What to Do When a Light Comes On

Do not ignore the light and do not simply reset it. The AA advises against both, and says restarting the engine can show whether a light remains but the fault should be checked by a mechanic or breakdown provider. Work through the same short routine every time. Note the colour and the symbol. If it is red, slow down, find a safe place and stop, then switch off and call for help. If it is amber, check the basics (oil level, coolant, tyre pressures) and book a garage visit within days, not weeks. If a light flashes, treat it as more serious than a solid one.

Check the car handbook for the exact symbols, as a few lights vary between manufacturers. A garage reading the fault code will tell you what is behind an amber light, and getting it done before the MOT avoids paying for a retest.

Sources

• RAC Drive: Dashboard warning lights: all symbols explained | RAC Drive
• The AA: Dashboard warning lights and what they mean | The AA
• What Car?: Car warning lights: understanding dashboard symbols and their meanings
• Blackcircles: Warning Lights & MOT Failures | Blackcircles.com
• GOV.UK: MOT inspection manual: cars and passenger vehicles – 1. Brakes – Guidance – GOV.UK
• GOV.UK: MOT inspection manual: cars and passenger vehicles – 7. Other equipment – Guidance – GOV.UK
• GOV.UK: MOT inspection manual: cars and passenger vehicles – 8. Nuisance – Guidance – GOV.UK