Tonight, as I was accelerating I heard a bang from the transmission, the ABS light came on and a minute later the transmission light came on. Ive had this happen to my E46, and usually I will turn the car off and back on and the lights will go off. Well, I turned the car off, and now it wont turn back on, it seems like the battery is dead too. Has anyone had this happen to them before?

 

Update. I was able to start the car 30min later, I drove around the block, the ABS and transmission light disappeared but now the Service Engline Light soon came on and increased emissions. I did some research and it seems like bad alternator or battery could be the issue. What do you guys think?

 

Standard Operating Procedure should be to run for codes... Whatever happened should be stored in the computer and is triggering your SEL. Its always a good starting point rather than throwing darts at a board blindfolded hoping to hit the correct spot.

You said it wouldnt start... did it do anything? Click, turn over... anything? Did you jump it to start it or did it miraculously decide to work after 30 minutes? Check the battery connections for corrosion and clean them so you have good contact if so.

 

+1000 on what Jaycal said. Also, since you said you heard a "bang" that does not indicate a battery issue unless it exploded (very rare). First thing I'd check are the belts, if the belt snapped on your alternator you will hear a bang and the car will die eventually running on battery alone. Definitely get the codes read, ASAP!!!!