Dodge Repair: No Overdrive, plymouth grand voyager, voyager 3

Question
I have 97 Plymouth Grand Voyager 3.3L, recently I took my car to a dealership to have the O2 sensor changed, ever since then my transmission shifts very hard and now it won't go into over-drive.  The service engine light recently came back on and it has a code 12 for the Throttle body sensor.  could the shifting have anything to do with the sensor.  Please help I am hesitant to take it back to the dealer.  

Answer
Code 12 does not relate to the throttle body sensors. is has to do with the battery, and the battery feed

I would recomend taking it back to the dealer and tell them you did not have this trouble before the repair and you want them to recheck what they did.  They could have left something unpluged or just not reset the computer after the repair.

Good luck,

Steve