WRX07

I had just left Ilkley after spending a week hol there.After 3 miles or so with 100 to go,the amber engine warning light came on.Luckily I had spotted a Subaru Dealer on the Leeds/Otley road.I pulled in,the car is an 07 WRX SL.The service guy said it was out of original 3 year waranty which is fair enough.They put the lap top on and reset the lamp but couldn't find the fault,still it cost me £50 to have it plugged in.The car has the Subaru extended waranty but because it has a K&N induction filter & stainless exhaust fitted (last Nov before I bought the car) they said this invalidated the waranty.The warning has not come on since,just a spurious alarm ?