Driver's guide
Check engine light on: what to do
It is the most common warning on the dashboard and it is not always serious. Here is how to tell an emergency from something that can wait a few days.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What the engine light is
It is the outline of an engine, usually yellow or orange. Its technical name is MIL (malfunction indicator lamp), and the engine control unit turns it on when it detects a fault that may affect emissions or how the engine runs.
When it turns the light on, the control unit stores a fault code (for example, P0420) and the data from the moment it happened. That code is the clue to what is going on.
Steady or flashing: the difference matters
Steady: a fault has been recorded. If the car drives normally it is not usually an emergency, but read the code soon rather than leaving it for weeks.
Flashing: it usually means severe misfires, which can overheat and damage the catalytic converter. Slow down, do not accelerate hard and take the car to a workshop as soon as possible; if it is also jerking badly, stop somewhere safe.
If a red warning light comes on (temperature, oil pressure, brakes or battery charge), stop as soon as it is safe and switch the engine off: those warnings are more urgent than the engine light.
What to do as soon as it comes on
Notice how the car drives: loss of power, jerking, noises, smoke, a burning smell or the temperature rising are reasons to stop.
Check the simple things: the fuel cap properly closed (a loose cap after refueling can turn the light on) and, with the engine cold, the oil and coolant levels.
Read the fault code with an OBD reader and look it up in our glossary: you will see what it means, its common causes and whether you should keep driving.
Book the workshop with the code and, if you can, the report of the reading: it saves diagnosis time.
Will the car pass its inspection with the light on?
In many European countries the periodic technical inspection checks the warning light and reads the control unit through the OBD socket: with the light on or with emission faults the car will normally fail.
Clearing the code just before does not help either: after clearing, the readiness monitors stay incomplete until the car has completed its drive cycles, and the inspection sees that too.
How Diaglana helps
With an ECO-LITE in the OBD socket you see in your account the fault codes the device reads from your car, and you can ask your workshop for help: it checks the car remotely, always with your permission.
Next step: find out which code it is
With the code in front of you, the glossary tells you what it means and how urgent it is.
Read your car's fault codes on your phone
With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.
Keep reading
- OBD fault codes: what each one means
- How to read and clear your car's fault codes
- Will your car pass its MOT or inspection with the engine light on?
- Wi-Fi OBD2 reader: which one to choose
- Reading fault codes by car make
- Remote OBD diagnostics: what it is, how it works and what it can't do
- Vehicle diagnostics glossary