When your car fails the MOT on emissions, it means your vehicle produces pollutants above the acceptable limit. Emissions checks are part of the MOT test to make sure vehicles meet environmental standards. These tests are designed to monitor gases like carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), which are harmful to air quality and public health.
Petrol and diesel engines are tested differently. Petrol vehicles are checked for CO and HC levels, while diesels go through a smoke density test. If your car doesn’t meet the required levels, it will not pass the MOT, rendering it illegal to drive until the issue is resolved.
Common Reasons Your Car Fails MOT on Emissions
If your car is flagged for MOT emissions failure, it’s often linked to underlying mechanical or fuel-related problems. Here are some of the usual suspects:
- Worn Spark Plugs: In petrol cars, old or dirty spark plugs lead to incomplete combustion, which increases emissions.
- Leaking Fuel Injectors: When injectors leak, too much fuel enters the engine, making emissions worse.
- Malfunctioning EGR Valve: The Exhaust Gas Recirculation (EGR) valve reduces NOx emissions in diesels. If it’s clogged or stuck, levels can spike.
- Old Engine Oil or Air Filters: Dirty filters and degraded oil can affect the way your engine burns fuel.
Understanding the cause can guide your next steps.
What to Do If a Car Fails MOT
If you’re unsure what to do if your car fails an MOT, follow these steps to stay compliant and make informed choices:
- Get a Detailed Failure Report: Your MOT testing centre will issue a VT30 ‘Refusal of an MOT Test Certificate’. This document lists the reasons for failure; emissions-related ones will be clearly highlighted.
- Book a Retest After Repairs: Once you know the cause, you can have the issue fixed by a trusted mechanic.
- Consider a Full Diagnostics Check: If the fault isn’t obvious, a diagnostics scan will pinpoint the sensor or part causing the problem. This is especially useful if warning lights (like the engine management light) are on.
- Drive Only to and from the Garage: Driving a car with a failed MOT is illegal, unless you’re heading directly to a pre-booked repair or retest. Be careful, as being stopped without proof could lead to fines or penalty points.
Is Fixing Emissions Failure Worth It?
It depends on your car’s age, condition, and market value. Repairs for MOT emissions failure can range from a £50 spark plug replacement to a £500+ DPF or catalytic converter fix.
If your car is old, high-mileage, or already has other issues (like rust or suspension problems), it might not be worth repairing.
Indicators: It’s Better to Scrap Than Repair
While some emissions issues are minor, others may not be worth addressing, especially if your car is already past its prime.
- Multiple MOT Failures: Failing more than once is a red flag. If your car has a history of issues, it might not get any better.
- High Repair Costs: If fixing the emissions problem costs more than the value of the car, it’s time to weigh other options.
- Low Resale Value: Even if you fix it, the resale value may not justify the expense. Scrapping could actually get you more cash.
- Major Component Failures: Emissions failure plus engine, suspension, or electrical faults? It’s rarely worth saving such a car.
- You Drive in Low-Emission Zones: If your car isn’t ULEZ compliant, repairs won’t change that. Better to scrap and switch to something greener.
How to Prepare for an MOT Retest After Emissions Repairs
If you’re fixing the problem and planning a retest, make sure the following are checked:
- Engine Warm-Up: A cold engine can produce higher emissions. Make sure it’s warmed up before the test.
- Use Additives: Fuel system cleaners can help reduce carbon buildup.
- Drive Regularly: If your car has been sitting idle, short trips won’t help. Take a long drive before testing.
- Check Warning Lights: If the engine management light is on, your car will fail, regardless of emissions readings.
- Service the Vehicle: A basic oil change and air filter replacement can make a difference.
Can You Sell a Car That Failed Its MOT on Emissions?
Yes, but your options are limited. Private buyers usually avoid non-MOT vehicles. Dealerships might offer a low trade-in value. However, scrap and salvage companies will take cars in any condition, including those that failed emissions tests.
Scrap a Van That Fails Emissions
Vans fail MOTs too, and often for similar emissions-related problems. If your commercial van is flagged, you have two options: repair or scrap. Repairs are often costlier for vans, especially diesel models with DPF issues. If you run a business, downtime is also a cost.
Scrapping offers a fast way to clear old fleet vans or write-offs from your site without extra paperwork or delay.
Final Thoughts
An MOT emissions failure isn’t the end of the road. Simple issues like spark plugs or filters can often be fixed at a modest cost, while larger faults such as catalytic converters or DPFs may demand a bigger investment. The decision to repair or scrap depends on your car’s overall condition, repair history, and long-term value. If the costs outweigh the benefits, scrapping may be the most practical step. Taking an honest look at repair expenses, resale value, and environmental compliance will help you make the right choice for both your budget and peace of mind.
Skip the stress and sell to a reliable scrap company. Scrap My Car online in the UK offers top quotes and instant pickup. If you want to sell a van for scrap, we make it quick, legal, and hassle-free. Get your free quote now!
