Good catch. I had not seen that light, ever, but I checked our '07 X3 owner's manual and it is listed.

However, it appears that the SES light is also involved. The manual says that the SES light will come on if the cap is opened while the engine is still running, and that the check gas cap light will come on if the gas cap is left loose after the vehicle is restarted.

Seems a bit complicated to me, but I guess it kept another design engineer employed for a few weeks.

I don't know for sure, but I suspect that the gas cap light is triggered by a mechanical contact on the cap, and that the SES light is triggered as always, by an out-of-range pressure reading in the fuel tank and carbon canister evaporative emission control system, most usually caused by a loose cap or cracked hose. It appears that this may have been the problem the OP had if in fact reseating the gas cap fixed it; if not, I would still go with a sensor as the most likely culprit.

Thanks for the post, DWill.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue