As regards to the code, the reading shows P0500. I can reset it and the car performs as it should in sport mode but a short time after it reverts back to the flashing arrow and sport and economy lights flashing and drives in economy mode.

I'm running 205 55 16s on the rear and 205 50 16s on the front

I have bought a 1996 850 t5 auto estate which is currently fitted with 55 profile tyres on the rear and 50's on the front. Could this be the cause of the transmission light arrow flashing on the dash as well as the sport and economy lights doing similar on the centre console. Thanks.