The Dieselgate scandal, which emerged in 2015, exposed the use of software designed to manipulate emissions test results in diesel vehicles. The fallout had a significant impact on vehicle regulation across the UK and Europe, including changes to MOT testing. Since then, MOT rules have evolved to place greater emphasis on real-world emissions, transparency, and environmental responsibility.
Dieselgate revealed that certain manufacturers had installed “defeat devices” allowing vehicles to pass laboratory emissions tests while producing far higher pollution levels during normal driving. This discovery raised serious concerns about air quality, public health, and the reliability of vehicle testing methods.
As a result, regulators introduced stricter oversight and improvements to MOT testing to ensure vehicles meet emissions standards in everyday use.
One of the most notable changes to MOT testing since Dieselgate is the tighter control of diesel emissions. The MOT diesel smoke test has been refined to detect excessive particulate emissions more accurately.
Vehicles now fail their MOT if they emit visible smoke of any colour during testing. This change aims to identify cars that may have malfunctioning emissions control systems or software manipulation, even if they previously passed under older rules.
MOT testers now pay closer attention to emissions-related components. Diesel particulate filters (DPFs), exhaust gas recirculation (EGR) systems, and catalytic converters are checked more carefully.
A missing or clearly tampered DPF is an automatic MOT failure. Warning lights related to emissions systems, such as the engine management light, can also result in a fail. These changes ensure that vehicles remain compliant throughout their lifespan, not just when new.
Since Dieselgate, MOT testing has become more alert to signs of modification or interference. Software remapping, removal of emissions equipment, or poorly executed repairs are more likely to be flagged during inspection.
While MOT testers cannot access vehicle software directly, visual checks, smoke testing, and dashboard warning light assessments help identify vehicles that may not meet legal standards.
With stricter testing in place, reviewing a vehicle’s MOT history has become increasingly valuable. Repeated emissions advisories or failures can indicate ongoing problems that servicing alone may not fix.
Using the MOT history checker on CheckMot.com allows drivers and buyers to spot trends, identify past emissions issues, and make informed decisions before purchasing or maintaining a vehicle.
The changes to MOT testing since Dieselgate support wider UK goals to improve air quality and reduce harmful emissions. By identifying high-polluting vehicles earlier, MOTs help remove unsafe or non-compliant cars from the road or prompt necessary repairs.
This benefits not only drivers but also communities, particularly in urban areas where air pollution poses the greatest health risks.
Yes. It prompted stricter emissions testing, better smoke detection, and increased scrutiny of emissions systems.
Indirectly, yes. If emissions controls are malfunctioning or warning lights are active, the vehicle can fail.
Diesel emissions checks are more robust than before, particularly for smoke and DPF compliance.
Only if they still meet emissions and safety standards. Poor remaps often lead to failures.
Review the vehicle’s MOT history online to see previous advisories and failures.