service engine light has been off and on for about a year.
SHOULD YOU REPLACE ALL OXYGEN SENSOR AT ONCE? on 2005 BMW 330Ci
try fuel system clean. ethanol treatment to 1 tank of premium. your car uses premium already how all fuel these days have ethanol blend mixed in. ethanol causes build up which can effect fuel delivery which effects the way your engine burns and exhausts and breaths. this accumulative effect can trip your sensors.
get a diag and do what is rec. no need to repl all sensors unless you have alot of extra money u are trying to get rid of
I agree with others that unless u have extra $$$ do what is necessary only, it is also obvious that with the check engine light being on for almost a year that this is not bothering the drivability of the vehicle,or is it? but it does sound like there may be more than what you are asking about , because what makes you want to consider changing all the O2 sensors? Secondly if the light has been on for this length of time it has probably set a code do get diagnostics test, sometimes it is the smallest problems that the driver leaves unattended, that give rises to a larger problem.