A brand spokesman told Autocar that the super-saloon model, which produces 425bhp from its turbocharged straight-six, would need a new particulate filter in order to meet the requirements of the new Worldwide Harmonised Light Vehicle Test Procedure (WLTP).
The rehomologation process that follows such a change would prevent the updated M3 from making it to market before the next-generation 3 Series is revealed in October. As such, BMW has chosen to pull the car early and end its production alongside the rest of the 3 Series range, rather than keep it in production for longer the way it has with its forebears.
No such scenario will be applicable for the M3’s two-door equivalent, the M4, because that car and its 4 Series siblings will remain on sale into the following year. The spokesman said that the M4 would go off sale “for a couple of months” while it is rehomologated, but that it would return to showrooms with its WLTP-certified filter.
The filter will reduce the car’s output of emissions to bring them below the maximum level required by the WLTP, but the spokesman said that performance would be unaffected. No other changes will be made to the tweaked M4, so it'll still be good for a claimed 4.3sec dash from zero to 62mph.
The decision to retain the M4 will also have been driven by its popularity. In Britain, close to 2400 M4s were sold in 2017, 700 of which were convertibles. Just 1100 M3s were sold in the UK last year.