Z4 2003 checked engine light

Quite often this code will appear due to improper seal on gas cap. Clean it well especially seal "O" ring and threaded part where it screws into filler pipe, add a little wipe of vaseline to "O" ring surface, and see if that doesn't cure it. Did you notice it soon after getting gas? Usually that's the case, but if that fails I'd try a new cap before spending big money on other new parts.