I am sure oil will have nothing to do with a engine code. Car is a 99 nissan motor is a 2.4 and code is po400 (stored code comes on almost daily). Its for the egr and egr valve is clean and good and maybe 2 yrs old. I have used carb cleaner in therein the port to clean and seems to help with the light staying off for awhile. This weekend i got some flexible wire and used it also. So question could the Valvoline Restore and Protect help or would it not? I dont think will help with this but wanted to ask