2.0 tdi brd pd170 yellow oil light has been coming on now for a while, oil is full every time. Today i took the cap off and the light went off which says to me pressure but the cap didnt blow out my hand or come off with force. Originally i thought it was a dodgy sensor before removing the cap. Could i have air in the system? Might be wrong but im sure this problem came up after a service , with oil change etc. No blue smoke and isnt running rough at all. No oil & coolant mix.