Hello,
yellow engine light is a warning light that could be several things.
i have a 2007 2.5 si and the first time that came on white smoke was coming out of the exhausts and the car was running in safe mode.Was a broken 5th cylinder that was replaced.Could you see if smoke is coming out of your car?
The second time yellow engine light came on was a broken thermostate that was replaced.
In both cases the car was connected and faults were read at the service that connected the car.
I suggest you rush to your bmw specialist to determine the problem.