Emissions are analysed by computer and compared to expected values. A failure means that there are excessive or high emission levels. This could be due to a failing catalytic converter or DPF, or a worn engine, or a faulty air to fuel ratio. Whatever the reason we can help determine what is causing the problem and get it fixed for you. Two standards exist for UK Exhaust Emissions. The first is Euro 4, which applies to any new model of vehicle approved for sale on or after 1 January 2005. It also applies to all vehicles for sale from 1 January 2007. Euro 5 updates the Euro 4 standard. It applies to all new models of vehicles available from 1 January 2011.

Once at steady idle the volume of exhaust smoke should be consistant and not excessive. If there's plumes of smoke being emitted from the tailpipe something is out of balance. Normal exhaust smoke should be thin pale whiteish once the engine is up to temperature, you would expect a stronger white vapour initially from a cold engine on initial startup. If there is coloured smoke after the engine has reached normal temperature, something is out of tolerance. Common colours indicating a fault are Black or Blue and less commonly Grey. Plumes of White may also indicate a problem.