- What the check engine light is telling you
- Steady, flashing or red: what each check engine light means
- Common causes of an engine management light
- Reading check engine light codes with an OBD scanner
- What to do when the check engine light comes on
- The engine management light and your MOT
- Related car know-how and where to share it
- Frequently asked questions
The check engine light, called the engine management light in the UK, means the car's sensors have detected a possible engine or emissions fault. A steady amber light usually means a less serious issue to get checked soon. A flashing or red light is more serious: pull over safely and call your breakdown provider.
An amber engine-shaped symbol suddenly glowing on the dashboard is enough to make most drivers' hearts sink. It's often called the check engine light, especially in the US. In the UK you'll more often hear it called the engine management light, or EML. Same light, same job: it's the car telling you its engine or emissions system has spotted something it doesn't like.
I've put this guide together from the AA's advice on the engine management light, the UK government's MOT inspection manual and Wikipedia's article about on-board diagnostics. Always check your car's handbook too, as what each colour means and what to do can vary between makes.
What the check engine light is telling you
The AA explains that the engine management light is usually shaped like an engine block and sits on the dashboard behind the steering wheel. Unlike most warning lights, it doesn't point to one specific fault. It comes on when the car's sensors detect a possible engine or emissions problem, and a faulty sensor can trigger it too.
It's normal for the light to come on briefly when you start the engine and then go out. The AA says that's normal. What matters is whether it stays on, and what colour and pattern it shows.
Steady, flashing or red: what each check engine light means
| What you see | What the AA says it suggests | What to do |
|---|---|---|
| Steady amber | A less serious issue, usually emissions related | You can normally finish your journey, then get it checked soon |
| Flashing amber | More serious, and may point to a problem affecting the catalytic converter | Get the car checked by a mechanic immediately |
| Steady red | A critical issue | Stop driving and contact your breakdown provider |
The AA adds that if the light's red or flashing while the engine's running, or you notice strange noises, reduced performance, smoke or unusual smells, you should pull over when it's safe, switch the engine off and report a breakdown.
Common causes of an engine management light
Because the light covers so many systems, the list of possible causes is long. The AA highlights these common ones:
- An oxygen sensor fault. The fuel mixture may be too rich or too lean, or the sensor itself has failed.
- A blocked diesel particulate filter (DPF). Or a fault with the sensor that monitors it.
- A mass airflow sensor problem. A damaged, blocked or missing air filter can upset it.
- An ignition fault. In petrol cars, faulty spark plugs or coils, which the AA says may make the light flash.
- A loose oil dipstick. If the light appears just after you've checked the oil, make sure the dipstick's pushed fully home.
The AA notes that low oil rarely triggers this light, because it has its own oil-can warning symbol.
Reading check engine light codes with an OBD scanner
When the light comes on, the car stores a diagnostic trouble code describing the fault. Wikipedia explains that modern cars use a standard system called on-board diagnostics. In the US it's OBD-II, and the European version is EOBD, which applies to petrol cars first registered in EU states from 2001 and diesel cars from 2004.
- The diagnostic port is a 16-pin connector, which Wikipedia says must be within 2 feet (0.61 m) of the steering wheel unless the manufacturer has an exemption.
- Codes are five characters: a letter followed by four characters. P stands for powertrain, C for chassis, B for body and U for network.
- EOBD codes look like P0 followed by three more characters, where the 0 shows it's a standard code.
- Simple code readers for drivers can read and clear basic codes, and some connect to a phone app by Bluetooth or USB.
A code tells you where to look, not always what's broken. The AA says identifying the fault needs diagnostic equipment, so a mechanic should find and fix it. Wikipedia warns that clearing a code doesn't fix the underlying problem and ignoring a serious fault can damage the engine.
What to do when the check engine light comes on
- Note the colour and whether it's steady or flashing.
- Check for other symptoms: strange noises, loss of power, smoke or unusual smells.
- If it's red, flashing or there are other symptoms, pull over when it's safe, switch off and call your breakdown provider.
- If it's steady amber with no other symptoms, the AA says you can usually continue to your destination, but avoid heavy acceleration and high engine speeds.
- The AA also suggests parking safely, waiting 2 minutes and restarting to see if the light stays on.
- Book the car in for a diagnostic check as soon as you can, even if the light goes off on its own.
The AA says the only guaranteed way to turn the light off is to fix the fault, and once a repair's done it goes off by itself. If it comes and goes, that usually means the fault is only detected at certain times, so it's still worth getting checked.
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The engine management light and your MOT
This one catches people out. The UK government's MOT inspection manual tells testers to switch on the ignition and check the engine malfunction indicator lamp lights up and then goes out. On some vehicles, the engine must be started before it goes off. If the lamp doesn't work, or it's showing a malfunction, that's a major defect, which means an MOT fail.
The manual applies this check to petrol cars, including hybrids, first used from 1 July, 2003 onwards (for vehicles with up to 8 passenger seats), and to diesel cars, including hybrids, first used from 1 July, 2008 onwards. So if the light's on, get the fault fixed before your test.
Related car know-how and where to share it
Warning lights and flat batteries are two of the most common reasons drivers end up at the roadside. If your car won't start at all, here's how to jump start a car safely using the RAC and AA guidance.
Mechanics and car writers will find automotive blogs that welcome contributed articles in my list.
Frequently asked questions
Is the check engine light the same as the engine management light?
Yes. Check engine light is the common US name and engine management light, or EML, is the usual UK term. The AA uses both names for the same dashboard warning.
Can I drive with the engine management light on?
The AA says that with only a steady amber light and no other symptoms you can usually continue to your destination and get it checked soon. If it's red or flashing, pull over safely and call for help.
Why is my engine management light flashing?
The AA says a flashing amber light is more serious and may point to a problem affecting the catalytic converter. On petrol cars, an ignition fault such as faulty spark plugs or coils can make it flash.
Will my car fail its MOT with the engine light on?
Yes. The MOT inspection manual lists an engine malfunction indicator lamp that's inoperative or indicating a malfunction as a major defect, which is a fail.
Can a code reader fix the check engine light?
A code reader can read and clear trouble codes, but clearing a code doesn't fix the fault. The AA says a mechanic with diagnostic equipment should find and repair the cause.
