We got this BMW X3 AWD,2004,a certified Pre-Owned one from Momentum dealership 4 days ago.It's got 97000 miles on it.and,since yesterday,this SERVICE ENGINE SOONlight has come up.What can be the problem?And is it safe to drive it with the light on?
We bought the extended warranty on it that is supposed to cover everything but tear and wears.And the dealership is one of the only two BMW dealerships in Houston.Actually,we just opened and closed the gas cap and the light went out.Could it be just the problem?

No reputable dealer would have CPO'd a vehicle with 97000 miles on it. Only vehicles still under the (then) 5 year 50,000 mile warranty are available for the BMW CPO program.

This vehicle needs to have the diagnostic system read out by a Certified BMW Diagnostic Technician and properly repaired. SES lights can indicate anything Emissions systems failure or out of acceptable limits or powertrain failure or out of acceptable limits.

If you left the gas cap loose then the evap tester would have read a leak in the system and reported a SES light...if you are at fault for leaving the gas cap off then just be sure to close it properly after each fill...if you are sure you closed it securely then have it replaced. *extended warranty is not the same as CPO* but this is an easy enough fix and an easy DIY