If you’re searching how to reduce emissions for MOT…
…Or asking “car failed MOT on emissions what can I do?” You’re likely dealing with an MOT emissions fail or preparing your vehicle to avoid one. This page offer all the information you should need to pass your MOT on emissions.
Reviews For our Services
Craig Harmieson
3 days ago
Amazing service, didnt expect too much but totally blew mind, performance was increased, not much but I'd recently had a new turbo, so didnt expect much, as for mpg, I was expecting afew mpg here or there, but in truth it blew my mind, I have a 2005 mondeo st estate with 162k on the clock, and it went from 45.4 mpg on motorways to 68.8, posted video as proof, should highly recommend
Emma Valentine
1 week ago
Couldn’t ask for better service. Had a carbon clean done this week on my partner’s Astra. Adrian responded very quickly to my initial query and got us booked in for the next day. He was very thorough and explained everything that I wasn’t sure of (my knowledge on cars is awful). He provided the fault codes and the live engine data and gave great advice about how to fix the current issue we were having with our car. The car runs very smoothly and is finally lovely to drive again, wish we’d done this sooner. He was very friendly & polite which put any worries I had at rest. I wouldn’t go anywhere else. Thank you so much!
Seagrave Media
1 week ago
"I recently had F5 Engine Carbon Clean work on my three vehicles—a 2012 BMW X1, 2007 Jaguar XJ, and 2005 Audi TT—and the results are superb.
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
Andrew Bailey
2 weeks ago
Highly recommend!!
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Charlie Stokes
2 weeks ago
Steve came out to give our DPF a full clean on our bmw 2 series the before and after results are incredible. More power better MPG and overall the car feels way better to drive. He showed us the before and after statistics. We are definitely getting him back to do a carbon clean
Amy Fryer-skelham
3 weeks ago
Our 3rd car being done by Adrian and always impresses us with the results . Very happy and will be lining number 4 up very soon
Ben Castle
3 weeks ago
Highly recommend this company.
Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.
Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.
Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Adam Brown
3 weeks ago
I rang Adrian after using him in the past and he got me booked in really quick, came out with constant updates on arrival time so didn’t have to sit around waiting. Did all the checks on the car then explained everything as it was being done, didn’t mind answering any questions asked. Mentioned a slight vibration and after it was all done the vibration was almost non existent sounded loads better and was driving in my opinion better. Really good job was very pleased and top man Thanks
Tim Ward
3 weeks ago
All round a very impressive service.There is a noticeable improvement in my 100k mile diesel, it runs more smoothly and hopefully will have a better mpg.
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Lewis Jones
4 weeks ago
Cant be happier with the service on my 115k mile 2013 Hyundai i30 1.6CRDi (Diesel). Quick responses on email/whattsapp. Open communication on how their van/machine needs to be setup and how to prepare your car. The clean was quick and Adrian was highly informative in the diagnostics with whats normal and whats irregular (luckily nothing major was found). Also told me about how the cleaning process works which was interesting. After the clean (~50mins) the car has an increase in performance, throttle response, a smoother operating engine with less vibration and improvements in the mpg (~10mpg) which were all previous problems I had encountered. Could not recommend them enough as it now feels like brand new and will certainly be using them again when the time comes around (~25k miles later as suggested) or if I were to change car.
eddie affection
1 month ago
Very polite very knowledgeable communication excellent carbon cleaned two of my vehicles with excellent results picked up a fault with one (hole in intercooler ) which I never would have found I put problem right and all is now good fantastic serviceView more
English Kernigit
1 month ago
Originally wanted a dpf clean but after speaking with Adrian, he recommended a carbon clean of my 2014 Mercedes sprinter. Turned up on time and with all the kit. Job done within the hour with some issues identified (new thermostat needed being chief). Almost immediately, my van runs smoother and quieter. Very happy with the results and equally with Adrian's no nonsense knowledge of the task and professionalism. Would definitely recommend you speak to him before anyone else.
emissions fail MOT result
An emissions fail MOT result can feel frustrating, especially if the vehicle seems to be driving normally. The good news is that most emissions MOT fail cases can be diagnosed and resolved properly when the root cause is identified.
Why Do Cars Fail MOT on Emissions?
When your vehicle fails on emissions, it means the exhaust gases exceed the legal limits for your engine type.
An mot emissions fail can be caused by:
- High carbon monoxide or carbon dioxide levels
- Lambda imbalance
- Incomplete combustion
- DPF regeneration issues
- Sensor faults
- Thermostat issues (engine running too cool)
Emissions don’t suddenly increase overnight unless there is a component failure. They typically rise gradually as engine efficiency declines through carbon buildup in the combustion chamber; something that regular engine carbon cleaning can address.
Car Failed MOT on Emissions – What Can I Do?
If your car failed MOT on emissions, the first step is not guessing. It’s diagnosing.
Here’s what you should do:
1. Identify the Type of Emissions Failure
Diesel Vehicles typically fail due to:
- High opacity or smoke levels
- DPF/GPF issues
- Excessive soot levels
Petrol Vehicles typically fail due to:
- High hydrocarbons
- High carbon monoxide
- Catalyst inefficiency
Understanding the failure reading is essential before taking action.
2. Check for Warning Lights
If your vehicle has:
- Engine management light on
- DPF light on
- Glow plug warning light
These can directly contribute to an emissions fail MOT result.
Driving harder will not correct emissions if supporting systems are faulty.
3. Ensure Proper Operating Temperature
An engine running too cool produces higher emissions.
A faulty thermostat is a very common cause of emissions MOT fail cases. If the engine never reaches proper operating temperature, combustion becomes inefficient and emissions increase.
4. Restore Combustion Efficiency
Over time, carbon build-up inside combustion chambers, injector tips and turbo components reduces combustion efficiency.
This can lead to:
- Increased fuel consumption
- Black smoke
- Higher soot output
- Failed MOT on emissions
A professional engine carbon cleaning service can help restore lost combustion efficiency and regular preventative maintenance engine carbon cleaning helps maintain your vehicle at its best.
Reviews For our Carbon Cleaning, DPF & Engine Diagnostics Services
Craig Harmieson
3 days ago
Amazing service, didnt expect too much but totally blew mind, performance was increased, not much but I'd recently had a new turbo, so didnt expect much, as for mpg, I was expecting afew mpg here or there, but in truth it blew my mind, I have a 2005 mondeo st estate with 162k on the clock, and it went from 45.4 mpg on motorways to 68.8, posted video as proof, should highly recommend
Emma Valentine
1 week ago
Couldn’t ask for better service. Had a carbon clean done this week on my partner’s Astra. Adrian responded very quickly to my initial query and got us booked in for the next day. He was very thorough and explained everything that I wasn’t sure of (my knowledge on cars is awful). He provided the fault codes and the live engine data and gave great advice about how to fix the current issue we were having with our car. The car runs very smoothly and is finally lovely to drive again, wish we’d done this sooner. He was very friendly & polite which put any worries I had at rest. I wouldn’t go anywhere else. Thank you so much!
Seagrave Media
1 week ago
"I recently had F5 Engine Carbon Clean work on my three vehicles—a 2012 BMW X1, 2007 Jaguar XJ, and 2005 Audi TT—and the results are superb.
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
Andrew Bailey
2 weeks ago
Highly recommend!!
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Charlie Stokes
2 weeks ago
Steve came out to give our DPF a full clean on our bmw 2 series the before and after results are incredible. More power better MPG and overall the car feels way better to drive. He showed us the before and after statistics. We are definitely getting him back to do a carbon clean
Amy Fryer-skelham
3 weeks ago
Our 3rd car being done by Adrian and always impresses us with the results . Very happy and will be lining number 4 up very soon
Ben Castle
3 weeks ago
Highly recommend this company.
Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.
Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.
Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Adam Brown
3 weeks ago
I rang Adrian after using him in the past and he got me booked in really quick, came out with constant updates on arrival time so didn’t have to sit around waiting. Did all the checks on the car then explained everything as it was being done, didn’t mind answering any questions asked. Mentioned a slight vibration and after it was all done the vibration was almost non existent sounded loads better and was driving in my opinion better. Really good job was very pleased and top man Thanks
Tim Ward
3 weeks ago
All round a very impressive service.There is a noticeable improvement in my 100k mile diesel, it runs more smoothly and hopefully will have a better mpg.
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Lewis Jones
4 weeks ago
Cant be happier with the service on my 115k mile 2013 Hyundai i30 1.6CRDi (Diesel). Quick responses on email/whattsapp. Open communication on how their van/machine needs to be setup and how to prepare your car. The clean was quick and Adrian was highly informative in the diagnostics with whats normal and whats irregular (luckily nothing major was found). Also told me about how the cleaning process works which was interesting. After the clean (~50mins) the car has an increase in performance, throttle response, a smoother operating engine with less vibration and improvements in the mpg (~10mpg) which were all previous problems I had encountered. Could not recommend them enough as it now feels like brand new and will certainly be using them again when the time comes around (~25k miles later as suggested) or if I were to change car.
eddie affection
1 month ago
Very polite very knowledgeable communication excellent carbon cleaned two of my vehicles with excellent results picked up a fault with one (hole in intercooler ) which I never would have found I put problem right and all is now good fantastic serviceView more
English Kernigit
1 month ago
Originally wanted a dpf clean but after speaking with Adrian, he recommended a carbon clean of my 2014 Mercedes sprinter. Turned up on time and with all the kit. Job done within the hour with some issues identified (new thermostat needed being chief). Almost immediately, my van runs smoother and quieter. Very happy with the results and equally with Adrian's no nonsense knowledge of the task and professionalism. Would definitely recommend you speak to him before anyone else.
Common Reasons for MOT Emissions Failures
From experience, the most common causes of emissions fail MOT results include:
- Carbon build-up
- DPF regeneration disabled
- Glow plug system faults
- Exhaust temperature sensor faults
- DPF pressure sensor faults
- Thermostat failure
- Catalyst deterioration
Diesel Emissions MOT Fail – What Happens?
If your diesel vehicle has an emissions MOT fail, it may show:
- Excessive black smoke
- Opacity readings too high
- DPF system fault
Simply driving at high revs before a re-test will not solve the issue if regeneration is disabled or if underlying faults exist.
Live data diagnostics are essential to confirm:
- Whether regeneration is possible
- Whether temperature conditions are correct
- Whether supporting components are functioning
Petrol vehicles may experience:
- High hydrocarbon levels
- High carbon monoxide
- Lambda imbalance
- Catalyst inefficiency
Carbon accumulation and combustion inefficiency can contribute, but sensor faults and thermostat issues are also common contributors.
How to Reduce Emissions Before MOT Re-Test
If your vehicle is due for MOT then it is an ideal time to book in with us for a live data engine diagnostic and engine carbon clean. This will allow us to sit down together with you to :
- Carry out a diagnostic inspection
- Identify any mechanical or sensor faults
- Confirm regeneration capability (diesel)
Perform an engine carbon clean to restore combustion efficiency as well as get it running smooth, quiet , responsive and economical again.
Does Carbon Cleaning Help with MOT Emissions Failures?
Yes it does.
By cleaning up the combustion chamber, injector tips , pistons , cylinders and cats it helps reduce emission levels.
Be aware though that depending on any underlying issues it may also need those issues fixing before it will pass completely.
It is not a substitute for repairing faulty components, hence Engine carbon cleaning should always be accompanied with proper live data diagnostics.
Reviews For our Carbon Cleaning, DPF & Engine Diagnostics Services
Craig Harmieson
3 days ago
Amazing service, didnt expect too much but totally blew mind, performance was increased, not much but I'd recently had a new turbo, so didnt expect much, as for mpg, I was expecting afew mpg here or there, but in truth it blew my mind, I have a 2005 mondeo st estate with 162k on the clock, and it went from 45.4 mpg on motorways to 68.8, posted video as proof, should highly recommend
Emma Valentine
1 week ago
Couldn’t ask for better service. Had a carbon clean done this week on my partner’s Astra. Adrian responded very quickly to my initial query and got us booked in for the next day. He was very thorough and explained everything that I wasn’t sure of (my knowledge on cars is awful). He provided the fault codes and the live engine data and gave great advice about how to fix the current issue we were having with our car. The car runs very smoothly and is finally lovely to drive again, wish we’d done this sooner. He was very friendly & polite which put any worries I had at rest. I wouldn’t go anywhere else. Thank you so much!
Seagrave Media
1 week ago
"I recently had F5 Engine Carbon Clean work on my three vehicles—a 2012 BMW X1, 2007 Jaguar XJ, and 2005 Audi TT—and the results are superb.
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
What really sets them apart is the comprehensive diagnostic work they carry out as part of the service. On two of my cars, the diagnostics highlighted a couple of underlying issues that I was completely unaware of. Because these were caught early, I was able to get them resolved alongside the carbon clean, which has made a massive difference to the overall performance.
All three cars now idle more quietly, feel sharper, and pull much more smoothly. It’s rare to find a service that combines deep technical knowledge with such tangible results. Professional, thorough, and highly recommended!"
Andrew Bailey
2 weeks ago
Highly recommend!!
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Excellent service, Adrian turned up on time, had the carbon clean and my car was diagnosed with a DPF issue so had a follow up appointment by Leon to sort out the issue and as I said before the car is much improved MPG seems back to normal and the car is running great.
Many thanks ????????
Charlie Stokes
2 weeks ago
Steve came out to give our DPF a full clean on our bmw 2 series the before and after results are incredible. More power better MPG and overall the car feels way better to drive. He showed us the before and after statistics. We are definitely getting him back to do a carbon clean
Amy Fryer-skelham
3 weeks ago
Our 3rd car being done by Adrian and always impresses us with the results . Very happy and will be lining number 4 up very soon
Ben Castle
3 weeks ago
Highly recommend this company.
Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.
Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Van was very sluggish and noisy so thought I would try a carbon clean and diagnostics.
Adrian was very quick to respond to my enquiry and managed to fit me in the same week. Adrian was incredibly knowledgeable and ran through the diagnostics with me and answered any questions I had. Carbon clean was quick and effective.
After the carbon clean the van drove a lot better and pulled through all gears very smoothly.
Well worth doing.
Adam Brown
3 weeks ago
I rang Adrian after using him in the past and he got me booked in really quick, came out with constant updates on arrival time so didn’t have to sit around waiting. Did all the checks on the car then explained everything as it was being done, didn’t mind answering any questions asked. Mentioned a slight vibration and after it was all done the vibration was almost non existent sounded loads better and was driving in my opinion better. Really good job was very pleased and top man Thanks
Tim Ward
3 weeks ago
All round a very impressive service.There is a noticeable improvement in my 100k mile diesel, it runs more smoothly and hopefully will have a better mpg.
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Adrian also took time to examine a number of engine fault codes, listing them for me for further investigations.
Thank you!
Lewis Jones
4 weeks ago
Cant be happier with the service on my 115k mile 2013 Hyundai i30 1.6CRDi (Diesel). Quick responses on email/whattsapp. Open communication on how their van/machine needs to be setup and how to prepare your car. The clean was quick and Adrian was highly informative in the diagnostics with whats normal and whats irregular (luckily nothing major was found). Also told me about how the cleaning process works which was interesting. After the clean (~50mins) the car has an increase in performance, throttle response, a smoother operating engine with less vibration and improvements in the mpg (~10mpg) which were all previous problems I had encountered. Could not recommend them enough as it now feels like brand new and will certainly be using them again when the time comes around (~25k miles later as suggested) or if I were to change car.
eddie affection
1 month ago
Very polite very knowledgeable communication excellent carbon cleaned two of my vehicles with excellent results picked up a fault with one (hole in intercooler ) which I never would have found I put problem right and all is now good fantastic serviceView more
English Kernigit
1 month ago
Originally wanted a dpf clean but after speaking with Adrian, he recommended a carbon clean of my 2014 Mercedes sprinter. Turned up on time and with all the kit. Job done within the hour with some issues identified (new thermostat needed being chief). Almost immediately, my van runs smoother and quieter. Very happy with the results and equally with Adrian's no nonsense knowledge of the task and professionalism. Would definitely recommend you speak to him before anyone else.
Case Study: Emissions MOT Fail Resolved
We recently saw a vehicle that had an emissions fail MOT result.
Diagnostics identified:
- Combustion inefficiency
- Thermostat fault preventing correct operating temperature
The vehicle underwent thermostat replacement and professional carbon cleaning.
The result:
- Reduced emissions
- Smoother running
- Successful MOT pass
Addressing both efficiency and mechanical faults was key.
Avoid:
- Ignoring the root cause
- Re-testing without investigation
- Random additive treatments
- Assuming the DPF or Catalytic Converter needs immediate replacement
This often leads to repeat failure and additional cost.
How to Reduce Emissions for MOT
If you’re asking:
- How to reduce emissions for MOT
- Car failed MOT on emissions what can I do
- MOT emissions fail
- Emissions fail MOT
The answer is always the same:
Start with diagnostics and with vehicles with over 20,000 an engine carbon clean to clean up the engine.
Understanding what is causing elevated emissions allows the correct solution to be applied safely and effectively.
Most emissions MOT fail cases are resolvable when the root cause is identified early.
Our Approach
☑️ Full live data diagnostics
☑️ Honest advice, no unnecessary cleaning
☑️ Which? Trusted Trader approved
☑️ Fully insured and IMI Certified