The engine management light (EML) comes on when your car's engine control unit detects a fault, from something minor like a loose petrol cap to something serious enough to need immediate attention. Whether it's safe to keep driving depends on the colour and whether it's flashing, covered below. This guide explains what the light means, how to tell if it's safe to drive, what commonly causes it, how to find the fault, and how to reset it once the issue is fixed.
Please note:
- Before you work on your vehicle or disconnect the battery, please refer to your vehicle handbook for guidance first.
- You should always check your vehicle handbook for any fault remedy before carrying out any work on your vehicle. If you are unsure of what is required to fix any problems, please consult a professional.
- If you see a red engine management light, it means your engine has a serious fault and you should pull over and seek roadside assistance.
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What is an Engine Management Light (eml light)?
The engine management light is one of your vehicle’s dashboard warning lights.
An amber or red EML (also called the check engine light) lets you know there's an issue with the engine.
What Does the Engine Management Light Look Like?
The EML usually displays as an engine block or, in some vehicles, as "check engine" wording and appears on the dashboard behind your steering wheel.
Some cars display the warning light in different colours according to how serious the problem is.
Many cars only ever show the EML in amber, the colour used and what it means both vary by manufacturer, so always check your vehicle handbook for the precise definitions.
Is It Safe to Drive With the Engine Management Light On?
EML state and what to do:
EML state | What it usually means | What to do |
Solid amber | A fault, often not urgent | Usually safe to continue carefully and get it checked soon |
Flashing amber | Often a misfire | Reduce speed and stop as soon as it's safe |
Red (solid or flashing) | A serious fault | Stop safely and call for roadside assistance |
Note: colours and flashing behaviour vary by manufacturer, check your handbook if you're unsure what your car's EML is telling you.
If your engine management light is flashing, this often signals a misfire, reduce speed and stop driving as soon as it's safe to do so, rather than continuing your journey.
What Can Cause the Engine Management Light to Come On?
The EML can come on for a number of reasons, where some can be minor, some requiring a mechanic. Common causes include:
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Loose Petrol Cap
A loose petrol cap is one of the most common causes for the EML to come on.
Check the cap to see if it is damaged. If it is, replace the cap with a new one.
Oxygen Sensor
Your EML may come on if the oxygen sensor detects your car is running fuel which is too rich or too lean.
There may also be a fault with the sensor. This can be remedied by reprogramming/recalibrating the engine control unit (ECU). Your mechanic will be able to do this for you.
Diesel Particulate Filter (DPF)
Your EML may come on if there is a fault with your DPF - a filter that captures and stores exhaust soot and essentially helps make your engine less polluting.
A faulty differential pressure sensor may also mean the car's engine control unit doesn't know the status of the diesel particulate filter, which could cause the EML to come on.
Mass Airflow Sensor
The mass airflow sensor is essential for your car's performance. This sensor helps your engine run efficiently.
The ECU needs data from the mass airflow sensor to determine how much fuel to add to the combustion chambers so it matches the amount of air flowing into the engine.
A missing, clogged or damaged air filter can itself damage the mass airflow sensor and cause the EML to come on.
Ignition System
In a petrol car, issues with your ignition system's spark plugs or coils may cause the EML to come on.
Finding Out What the Fault Is
Use an OBD2 On-Board Diagnostic Scanner
The easiest way to determine a fault causing the EML to come on is to use an OBD-II scanner (on-board diagnostic scanner).
This device can be purchased online for around £20.
Simply connect the OBD2 scanner to the connection port, which should be located under your dashboard on the passenger side. Almost all cars built after 2000 have this port.
How to Use an On-Board Diagnostic Scanner
After connecting the OBD2, turn off all connected gadgets then turn on your ignition.
Press the "READ" button and any error codes will be displayed.
Note down the codes then consult your car's handbook to find out what the fault is. If you don't have your handbook, the manual that came with the scanner should tell you what the code(s) mean.
Next, press "ERASE" (or "CLEAR" on some scanners), which will clear all the error codes. If all the error codes are cleared, the EML will go off.
Clearing the codes doesn't fix the underlying fault, if the problem is still there, the light will come back on.
What If You Don't Have an On-Board Diagnostic Scanner?
Alternatively, you may decide to take your vehicle to your local garage for engine light troubleshooting, where they will have an OBD2 diagnostics scanner. They will then scan the code and determine the issue with your EML.
How to Reset the Engine Management Light
Once you know what caused the EML and have fixed it (or are confident it was a one-off glitch), here's how to reset engine management light warnings:
Reset by Removing the Car Battery Cables
One of the best known methods to reset the EML is to disconnect your car's battery cables.
Use a wrench to remove positive and negative cables. Next, drain any residual current by holding down the horn for half a minute. Wait around 15 minutes, then reconnect the battery cables. Check the error codes have been deleted and the EML has gone off.
If the warning light returns, then you probably have an issue that requires the attention of a mechanic.
Alternatively, your local garage will be able to reset your EML.
Turn the Ignition On and Off
An even simpler way to clear the EML is to turn the ignition on and off. This approach achieves the same outcome as the previous step, but without disconnecting the battery.
Turn the ignition on and off three times, pausing a second between each cycle.
The EML should go off. If it doesn't, consult a mechanic.
Wait for the Light to Go Off
If you notice the EML has come on, you could wait a few days to see if it goes off by itself.
The warning light may come on due to some internal glitch. However, if the EML remains on after this period, you should take steps to determine the problem.
Note however, if your engine management light flashing, you may have a serious issue and should stop driving your vehicle.
Why Does My EML Come On When I Start My Car?
It is normal for the EML to illuminate with the ignition prior to starting, however, it should always go out once the car is running.
What Does It Mean If the Light Stays On?
If the EML remains on continuously, or is flashing after the ignition has started, then you may have a problem.
Unlike other dashboard warning lights, the EML can be harder to diagnose. This is because it doesn't alert you to a specific fault, so it's best to get your car checked over for any issues as soon as possible.
Engine Warning Light Has Come Back On
You may find that the EML goes off for a period, then returns.
Once again, this means you should take action to work out what the issue is that is causing it.
The easiest way to diagnose why the EML is coming on is to take your car to a mechanic.
Will My Car Fail Its MOT With the Engine Management Light On?
In short, no — your car will not pass an MOT if the engine management light is on. Searching "engine management light MOT" usually means wanting to know exactly this.
Stricter MOT rules were introduced in 2018 meaning any car undergoing an MOT test with an illuminated EML (whether it's a red or amber warning light) would automatically fail.
Taking Your Car to the Garage for Engine Light Issues
As mentioned, if any of these processes for how to reset an EML are outside of your mechanical/electrical knowledge, or if you simply do not have the time or inclination, then your local garage will be able to assist you in diagnosing and solving your issue and in undertaking an engine management light reset.
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