How to Reduce Car Emissions for an MOT
If you’re worried your car might fail its MOT on emissions, the good news is there are several simple things you can do to improve your chances of passing.
Emissions failures are increasingly common, but they’re often caused by build-up, poor maintenance, or short journeys . . which are all fixable issues.
Why emissions matter for an MOT
During an MOT, your car is tested to ensure it meets legal limits for exhaust emissions. If levels are too high, it can result in:
A Major fault (fail)
or even a Dangerous fault in severe cases
That means you will be unable to drive the car until it’s fixed.
Quick wins before your MOT (do these first)
If your test is coming up soon, start here:
Take the car for a longer drive
Short journeys cause carbon build-up in the engine and exhaust.
Before your MOT:
Drive for 15–30 minutes at higher speeds (e.g. motorway or A-road)
Keep the engine warm
This helps clear deposits and improves emissions.
Use a fuel system cleaner
Additives can help remove build-up inside the engine.
Pour into the fuel tank (follow instructions)
Drive normally to circulate it
Many premium fuels already include cleaning agents, so as your car gets older, switching to premium fuel might be a good idea.
Typically, the agent should be poured into the fuel tank when your car has at least a quarter-tank of fuel. Once you have applied the fluid, simply go for a 10-15 minute drive and allow the agent to be flushed through your engine.
Check your tyre pressure
It’s simple but often overlooked. Under-inflated tyres:
Increase fuel consumption
Increase emissions
Get into the habit of checking tyre pressure at least once a month.
Your owner's manual should have the recommended pressures listed (sometimes it's also printed somewhere in the glove box, where you can find it more easily). If pressures are below the indicated amount, simply top them up.
Replace the air filter
A clogged air filter restricts airflow and increases emissions. Signs it may need replacing:
Reduced performance
Poor fuel economy
It’s a low-cost fix that can make a noticeable difference.
If you are replacing this yourself, you'll need the correct replacement filter for your car model.
1. Ensure the engine is cool before starting, then open the bonnet
2. Locate the old air filter - it's usually in a housing that looks like a black plastic box next to the motor, with a large air duct protruding from it
3. Unclip or unscrew the metal locks holding the housing in place and gently remove the old filter and discard
4. Remove any pieces of dirt and debris; use a vacuum to remove any dust
5. Insert the new filter, rim facing upwards. Once the rubber rim is sealed around the housing, clip the cover back in place and re-fasten the screws or clamps to secure it
Common cause of MOT failures: the catalytic converter
Your catalytic converter reduces harmful gases before they leave the exhaust. If it’s not working properly, emissions will rise quickly.
Warning signs include:
Loss of engine power
Rattling noises underneath the car
A “rotten egg” smell
Dark exhaust smoke
Engine warning light
If you notice these, get it checked before your MOT.
What about diesel cars (DPF issues)?
For diesel vehicles, the Diesel Particulate Filter (DPF) is a common failure point. Short journeys can prevent it from regenerating properly.
Take a longer drive at steady speed
Allow the engine to reach full operating temperature
See more information on our guide to diesel cars here.
Ongoing habits to keep emissions low
Good maintenance reduces the risk of MOT issues:
Service your car regularly
Use quality fuel
Avoid repeated short journeys
Keep tyres properly inflated
Respond to warning lights early
Small habits make a big difference over time.
If your car fails on emissions
Don’t panic — many issues are fixable. Common fixes include:
Replacing filters
Cleaning fuel systems
Repairing or replacing sensors
Catalytic converter or DPF work
Fix the issue, then book a retest.
Maintenance vs MOT: what’s the link?
Your MOT checks whether your car meets legal standards. But it’s your responsibility to keep he vehicle maintained and get issues fixed before the test. Poor maintenance is one of the biggest reasons for MOT failure.
How leasing helps avoid MOT stress
One advantage of leasing is most cars are brand new, and therefore under warranty
That means:
Fewer mechanical issues
Lower emissions risk
No MOT required for the first 3 years
For many drivers, this removes a lot of uncertainty and cost.
Should you consider a maintenance package?
If you want to reduce the risk of MOT failures and unexpected repairs, then a maintenance package ensures that:
Servicing is done on time
Worn parts are replaced early
Issues are spotted before they become problems
You can add maintenance when setting up your lease or speak to our team about options.
Need a simpler way to avoid MOT headaches?
If you’re tired of dealing with emissions issues, repair bills or MOT uncertainty, leasing a newer, more efficient vehicle could be a smarter option.
Explore our latest car lease deals or speak to our team about low-emission and maintenance-supported options.