What to do if your emission light comes on

An amber symbol of an engine is glowing on your dashboard, but what does it mean? Every image on your dashboard has a purpose and when something lights up to indicate a potential problem, it shouldn’t be ignored. The check engine light, which signifies several possible issues including emissions, is the most common.

The check engine light (CEL) illuminates after being prompted by the engine control unit that manages the engine. If the control unit determines that something in your engine is not functioning properly, it will send the signal to light up the symbol on the dashboard. So, you see it blink to life, but what should you do?

Unlike certain symbols which tell you exactly what is wrong with your vehicle, such as the coolant temperature light that alerts you of overheating, the CEL can glow for several reasons. Because of this, you should take it to a garage for the technicians to determine the root cause and go from there.

As you won’t be immediately aware of the cause, there are several things you can do initially to try and solve the issue.

1. Observe

Check that there are no other symbols on your dashboard indicating additional problems, such as low oil pressure or overheating. If this is the case, pull your vehicle over, shut the engine off and contact a roadside service.

2. Check gas cap

Tighten or replace your gas cap as sometimes a broken or loose rubber seal can trigger the light to come on.

3. Reduce pressure

If you think that your vehicle feels different on the road, especially if the performance has decreased, reduce your speed and avoid transporting heavy goods.

4. Check whether the engine light is constant or flashing

A solid glow tells you that you should have your vehicle inspected soon, however a blinking CEL is a greater cause for concern and indicates that your vehicle should be inspected by a professional immediately.

What can cause the emissions light to come on?

There are several different possible triggers for an illuminated engine light. The following are some of the most frequent causes.

  • Emissions system fault

Your emissions control monitors the volume of carbon monoxide that your vehicle emits while in motion. This is something that people are becoming increasingly aware of by opting for more eco-friendly vehicles to reduce their carbon footprint. A component of this is the oxygen sensor, which can sense if the engine is burning too much or not enough fuel. This can trigger the CEL to indicate that the car is either running too rich or too lean, or that there’s an issue with the sensor itself.

  • Blocked diesel particulate filter

This function measures how easily gas is able to travel through the exhaust. As this gas moves through the system, it must pass through the particulate filter, which removes harmful particles from the exhaust. It does this by oxidising the particles into a fine ash. The CEL may illuminate if this process fails in some way, or if the filter becomes blocked.

  • Mass airflow sensor fault

The engine control unit calculates how much fuel to add to the combustion chambers based on data from the mass airflow sensor. This sensor gathers information from an air filter, which, if incorrectly installed or clogged, can damage the sensor. If this is the case, the CEL will appear.

  • Ignition system fault

Responsible for burning the fuel that starts an engine is the ignition system. Faults with components such as glow plugs, spark plugs and coil cylinders can all be indicated by the CEL. These kinds of faults are known as ‘misfires’ and repair often involves getting replacements.

How to reset an emission warning light

You should take your car to a garage, who will give it a full examination, solve the problem and turn off the light for you. If the light doesn’t turn off automatically, then you can try the following methods. It’s important that you get the problem fixed rather than simply resetting your light without looking into any potential causes.

The easiest method to reset the check engine light is to drive your car as you normally would and let the light turn off naturally by itself. If it hasn’t turned off after three days, turn the car on and off three times consecutively.

If the CEL still isn’t turning off, it’s time to disconnect and reconnect the battery. While the engine is not running, use a wrench to disconnect the positive power cable and leave it for 20 minutes. Turn the key in the ignition to the ‘ON’ position. Reconnect the positive battery cable and turn the key in the ignition, wait a few minutes and the CEL should be gone.

If neither of these work, it’s best to take your vehicle into a garage so that a professional can reset your light. They will also run proper diagnostics and find the exact cause behind it illuminating in the first place and determine if there are any issues with your car.

Can you drive with the exhaust emissions light on?

It is safe to drive with an amber check engine light glowing on your dashboard, especially if you cannot detect any problems with the smooth operation of the car. However, it’s always best to find the reason why it came on in the first place, even if that means taking it to be looked at by a professional. If the CEL glows up in red, that is greater cause for concern and you should pull over where appropriate and arrange for immediate inspection.