Diagnostics firm Topdon Europe has identified P0420 as the most common fault code in European cars, based on an analysis of over 340,000 active diagnostic platform sessions. The code relates to problems with a vehicle's catalytic converter, a component found on nearly every petrol and diesel vehicle in the UK.
Emissions and MOT Risks
Vehicles showing the P0420 code are likely to be producing more pollutants than allowed. This could be a serious issue for drivers, as emissions levels are checked during the annual MOT test. Cars found to be exceeding their limits would likely fail the MOT, forcing motorists to get the issue fixed to keep their vehicle on the road.
Expert Warning Against Clearing the Code
Oscar Diaz, CEO at Topdon Europe, stressed that some road users might simply clear the code during a diagnostic check without understanding what it means. He explained: “P0420 is the fault we see more of than any other across Europe, and it is a good example of where our tools are designed to help without overreaching.”
“An owner can read the code, understand what it means and know what they are being told. What they should not do is clear it and drive on. Emissions hardware exists for a reason, and a professional workshop is the right place to have it looked at,” Diaz added.
Potential Causes and Repair Options
The code could suggest various issues, including a worn-out catalyst, faulty oxygen sensor, or an exhaust leak. A P0420 could trigger the check engine light, but motorists are unlikely to notice major changes to driveability, meaning the issue may go undetected.
In the UK, all petrol cars registered since 1993 must be equipped with a catalytic converter. Garages will inspect the component and decide on repairs. If the catalytic converter is damaged, mechanics may need to replace it entirely. If it is still functioning, garages may replace a faulty sensor to better read exhaust gases.
