Had all fuel injectors and spark plugs replaced less than 10K miles ago. Not sure what else could cause this error.
Possible causes
- Faulty spark plug 6
- Clogged or faulty fuel injector 6
- Faulty ignition coil 6
- Fuel injector 6 harness is open or shorted
- Fuel injector 6 circuit poor electrical connection
- Ignition coil 6 harness is open or shorted
- Ignition coil 6 circuit poor electrical connection
- Insufficient cylinder 6 compression
- Incorrect fuel pressure
- Intake air leak
http://engine-codes.com/p0306_bmw.html
http://repairpal.com/OBD-II-Code-P0306