engine check light comes on and speedometer/ mileage counter do not

ok,thank you. now I have another problem with the same vehicle..there's a rattling noise coming from the engine. I was told that it May be a stuck lifter. it was suggested that I add a bottle of CD2 to my oil. I did this and it still the same. I asked another mechanic what else should I do he suggested I get new valve cover and that the problem was could probably be a broken spring in that area. My question to you is, how much is this going to cost and is it possible it could be something else? I'm on a budget and really depend on my vehicle to get me to & from work.