TannadiceMotors
Warning lights
What the common lights mean, how urgent they are, and what to do next — in plain English.
Red — stop when it’s safe and call us.
Amber — get it checked soon.
What it means: The engine’s computer has logged a fault — anything from a loose sensor to a misfire.
What to do: If it’s steady, the car is usually safe to drive gently to us for a diagnostic check. If it’s flashing, ease off and get it looked at straight away: a misfire can damage the catalytic converter.
A steady engine management light is an MOT fail (major) — on petrol cars first used from 1 July 2003 and diesels from 1 July 2008.
What it means: The anti-lock braking system has a fault. Your normal brakes still work, but the wheels can lock under hard braking.
What to do: Drive carefully, leave extra stopping distance and book a check. Common causes are wheel speed sensors and wiring.
An ABS light showing a system fault is an MOT fail (major), and so is one that does not light at all when you turn the ignition on.
What it means: Oil pressure is too low to protect the engine.
What to do: Stop as soon as it’s safe and switch the engine off. Check the oil level once it has cooled. Don’t keep driving — call us.
What it means: The charging system isn’t working, so the car is running on what’s left in the battery. Often the alternator or its drive belt.
What to do: Switch off anything you don’t need and head for the garage. Avoid stopping the engine somewhere you can’t get help.
What it means: One or more tyres is low, or the tyre pressure monitoring system has a fault.
What to do: Check and adjust all four pressures (the right figures are usually inside the fuel flap or door pillar). If it comes back, you may have a slow puncture.
A tyre pressure monitoring system that is malfunctioning is an MOT fail (major), on cars first used from 1 January 2012. A lamp simply telling you a tyre is soft is not, on its own, a defect.
What it means: The handbrake is on, the brake fluid is low, or there’s a fault in the braking system.
What to do: Check the handbrake is fully off. If the light stays on, don’t drive — low fluid can mean a leak. Call us.
A brake fluid level warning light that is on is recorded at the MOT as a minor defect, not a fail — but an electronic parking brake warning showing a fault is a fail.
What it means: The engine is running hotter than it should — usually lost coolant, a failed thermostat, a water pump, or a cooling fan that has stopped.
What to do: Stop as soon as it’s safe and switch off. An overheating engine can warp a cylinder head in minutes, which is a far bigger bill than whatever caused it. Don’t open the expansion tank while it’s hot — the system is pressurised. Let it cool right down before checking the level, and call us.
What it means: The diesel particulate filter is getting blocked with soot, which is common on diesels that do mostly short trips.
What to do: Your handbook will say how to let it clean itself — usually a steady drive at higher speed. If the light stays on, bring it in before it becomes a bigger repair.
What it means: There’s a fault in the airbag or seatbelt tensioner system, so they might not work in a crash.
What to do: The car will drive normally, but get it checked soon.
An airbag warning light showing a system fault is an MOT fail (major). The separate lamp that says the passenger airbag is switched off is not a defect — that one is doing its job.
This is general guidance. Symbols and colours vary between manufacturers — your handbook has the final word. If in doubt, don’t drive it: call 01382 690898.
Not all of them, and the rules are more specific than most people are told. These are failures, recorded as major defects:
A brake fluid level warning is different — it gets recorded, but as a minor defect rather than a fail.
A lamp that never comes on is also a fail. The tester turns the ignition on and watches the warning lights light up and then go out. For the engine management and ABS lamps, "not working" is a major defect in its own right — so removing a bulb, or a previous owner having removed one, fails just as surely as the light staying on. It is worth checking they all appear for a second when you switch on.
The passenger airbag lamp is not the airbag warning light. The one telling you the passenger airbag is switched off is doing exactly what it should, and the manual says in terms that it is not a defect. Likewise a tyre pressure lamp that is simply reporting a soft tyre — put some air in it rather than booking a diagnostic.
Red means stop, and the order matters more than the diagnosis:
Amber is different: it generally means carry on, gently, and get it looked at soon rather than now. The exception is a flashing engine management light, which means a live misfire — ease off and get it seen before it takes the catalytic converter with it.
You can, and it will come back, because clearing a code does not fix what set it. It also wipes the stored data that would have told us what happened, which makes the fault harder and more expensive to find. Better to have it read first.
Possibly, but the code usually stays stored even after the lamp clears itself. Having it read takes minutes and tells you whether something is still brewing.
Steady means a fault is logged and you should get it checked soon. Flashing means it is happening right now, normally a misfire, and continuing can destroy the catalytic converter. Ease off and get it looked at.
Symbols vary between manufacturers and your handbook has the final word. If you would rather ask a person, ring us and describe it — colour, rough shape, steady or flashing — or send a photo of the dashboard through the contact form.
Some will and some will not — engine management, ABS, airbag, electronic parking brake and tyre pressure monitoring can all be failures, with dates attached, while a brake fluid warning is only a minor defect. The section above sets out which is which.
Light still on?