So I was driving one night and out of no where my iDrive screen says "Increased Emissions" and the Service Engine Soon light turns on in the gauge cluster. I'm not sure what it could be, I scheduled an appointment to have it checked at my BMW dealership. Perhaps it could be the O2 Sensor? Thermostat? Has this happened to anyone..if so, what did it turn out to be? The engine continues to run like it always has, flawless. On a side note, one thing I did notice is that my MPG would always average between 20.8 MPG - 21.5 MPG for the last couple of years. Now, it displays 22.6 MPG constantly.

My car is a 2005 545i with 90k miles on it. All input/comments are appreciated.

Thanks

May be the thermostat or the crank case vent valve..........if it's the crankcase vent valve, there is a DIY for it, the thermostat is
also pretty easy to do. Either way, should be an easy fix.

I have had the same warning on and off for the past month and a half or so. Every time I take it to the dealership, they seem to make it go away; only for the warning to pop up again a week or so later. Has happened twice already, tomorrow will be a third. I heard or read somewhere that it could be the gas tank cap not being tightly closed. Not sure if this is true or not, but I have yet to make the warning light go away on my own without having to take it to the dealer.

same issue on my 04 530i came on a week abo hoping it was gas cap but still on ill see what the dealer says in a few days and post my solution for mine.

most likely thermostat

Mine was the crankcase vent valves. Under $50.00 in parts and you can find the diy stuff on here like stated before. My car started running rough after awhile (stalled when stopped) but at first I just had the warning light, for about a month.

Had the increased emissions warning a couple of months ago. I replaced the crankcase vent valves (one was torn) and cleaned the MAF sensor.

I took the car to a local indy shop and had the sensor reset, not a problem since then. The car ran fine while the emissions light was on, I think it was just a malfunction with the sensor.

That has happened to me a few times, and from what I remember it was always within a day of filling up with fuel. I then take the gas cap off, put it back on, and make it click 3 or 4 times to make sure its tight. Then within days it turns off and is fine.

Pretty funny that I have the same issue. I have a 2004 545i with 88k miles. I already replaced the gas cap and it did not fix. The thing is sometimes when I start my car the SES light doesn't come on and it wont for a few hours or so, then out of the blue it comes on again. I replaced the crank case valves on the heads and I noticed my idle got worse after replacing them. Maybe I did it wrong. I'm going to check them and make sure they are not damaged. Its the first time I hear anything about the thermostat. How can I test to see if it is good? I will post my findings.

Just a quick update to my situation: So I took my car to another dealer instead of the usual one I go to for servicing. I am still under the original extended warranty but the new (to me) dealer wants to charge me if it is infact the gas cap thing to reset the warning (increased emission. I told them that for the past three fill ups at the gas station I have opened and reclosed the fuel cap and tightened it accordingly. My old stealer would reset the warning free of charge. Are they charging me because I am new to them? It just so happens that I had to switch because the old dealer didn't want to do the software update to allow mp3 cd/dvd playback. I'm thinking I will just live with the service engine soon light warning due to increased emissions for a bit.