If your not shore leave it to the pros otherwise you could do more dommage to the engine like bend valves.
Pretty simple but if your not shore leave it to a garage fitting should cost no more then £40an a replacement unite should cost about £80.
It sounds like your engine management light has come one you need to get the car pluged in it should cost about £20 to £40 pound no need to go to vauxhall that will cost £80 , it is probably your E.G.R VALVE clean it out first.
Does it turn over? If the cam turns on most cars you can look through where the oil cap goes by removing the cap, if not you will have to remove the cam belt cover , don't forget to crank over the car wile looking.