ok...the car is 545i with 72k on it,check engine came on and stays on and also a message "emissions exceeded limits" pop on on the nav screen. Im thinking its an faulty O2 sensor but what do you guys think?


S.

 

sounds about right, but you need the dealer to do the work.

 

I would not assume right away its an O2 sensor. Was message on iDrive like you typed it or was it "Increased Emissions"?

 

Thermostat. I'd bet 50 bucks.

 

check the rubber crankcase valve on the top of the cylinder heads maybe

 

Emissions related parts are covered beyond the 4 yr / 50K miles. Check your warranty for parts and labor that are covered.

 

Had the light come on in mine. Took it to my independent and he couldn't find anything wrong. He reset it and it has not reoccurred.

 

Same car as mine: the previous two times this happened to me it was faulty thermostat.

 

I'd suggest to start replacing in the following order - thermostat, crankcase vent valves, temperature sensor at radiator outlet, temperature sensor at water pump. Replace one by one and reset CEL each time and wait if you get CEL again. It might be weeks, but might be month before you get another one, so just take it slow and don't replace all in one shot. Just a warning, that it might trigger chain effect on other parts. In my case engine was running cold and after all the replacements engine temperature went back to normal, but triggered weak parts failures in the cooling system - expansion tank cracked and plastic pipe (vent pipe running on top of the radiator) snapped.