I see its been answered... the seal around the petro cap can wear out... just look at rubber bands sitting out for a few months... they just fall apart. Its just a guess on my part I never replaced my petro cap before...

 

Another cause for this error is overfilling the tank, to the point that gas gets into the charcoal canister. If that's the case, it will clear in a day or so.

I had this happen twice on my wife's X3, The pump didn't shut off soon enough, and it overfilled the tank.

 

I checked the seal around the gas cap and everything seems to be as pristine as when I took delivery. As far as overfilling the tank, once I learned (early on) about gas expansion and vapors in the tank, I've always paid attention to when that tank goes "click" or at the very least listen for the sound of near full.

 

You might just have a small leak elsewhere in the system, or perhaps on the gas cap. The leak standards are very stringent; you might no see the defect in the seal, or perhaps the seal is not engaging properly.

I once interviewed an engineer that worked at a plant that made gas tanks. They check each tank for leak using helium. They fill the tank with helium, and have sensitive instruments on the outside to detect the sightest trace of helium. Helium is used because it is a very small molecule, it will leak out of smaller holes than other molecules, and is far more sensitive than a pressure decay test. When they upgraded the tests to the latest emissions standards around 2003 or so, they found that they got false positive tests due to the amount of helium that naturally occurs in the environment. To put this in perspective, helium makes up about 0.000524% of air. Clearly, the evaporative emissions standard is very stringent, and explains why you 5er has a charcoal filter on the intake, to prevent emissions from leaking out through the intake when the motor is off.

To finish the story, they ended up having to fill the area around the tank with pure nitrogen, so that they would avoid false positives from the atmosphere.

This is why you can make the claim that a modern car produces less pollution running than a car from the 70's makes parked with the engine off.

 

Wow, learn something new everyday. Reminds me of the top gear episode where Clarkson drove the Porsche 911 Turbo (997) and said pretty much the air coming out was cleaner than the air coming in.

In the course of checking things off their list, how soon would the SES light go out if the dealer just replaced the gas cap (and that was the cause of the problem)? I have a loaner set up just in case they have to go as far as taking a fuel sample and removing the gas tank to find the source of the problem. Since I live ~45min from the dealer, I'm feeling that by the time I get home the car will be ready.

 

sounds lke a nightmare....hopefully is nothing serious

 

Update:

Got the car back. Service department said it was a faulty thermostat sensor.

DubyaTeeEff?? A thermostat sensor = increased emissions?

 

I had the same message on my 2004 525i last week.. I took it in for service and they told me my secondary air sytem needed to be reprogrammed. It had nothing to do with the gas I used was a computer issue.

 

I had an Increased Emissions error on my '05 525i and the dealer determined that it was an O2 sensor (Oxygen sensor for those who never took chemistry ).


This was covered under warranty at Motorwerks BMW in Bloomington, MN.

 

if it was the gas cap i remember seeing it on the idrive it will say please tighten gas cap. Wow a thermostat caused the increase in emissions huh, I know the Coolant temperature sensor can cause an increase in emission if it's not working properly, so since it's related possible it can be an issue. So you had it fixed already.