I had a check engine light on my diesel for 3 months waiting on an air temp. sensor. Mine also checked okay with the I drive. Sounds like you need to take it to the dealer. I waited 5 weeks for my fuel line heater to be replaced. Taking it in tomorrow. I had to call BMWNA both times to get the parts shipped to fix my vehicle. This last time, I've asked BMW to purchase my vehicle back. They called back 5.5 hours later to let me know they located a part for my vehicle and it would be at my dealer in two days. I find this unacceptable to have to call BMW every time I need a part ordered for my vehicle. Let us know if you have the same experience with your diesel. Also, let us know what the dealer finds when they hook your car up to their computer.

Hope you have better luck than I've had with mine...

Craig