the first time the engine management light came on, the petrol gage was on red the light stayed on after i filled petrol tank up, . then i took it to my local garage and he changed the cam sensor, everything was fine for about two weeks,petrol hit the red again and light came back on, and stayed on even when i filled the car back . any ideas what it could be? i heard it could be the timing chain and i believe that it would be a big pricey job??