1997 Dodge Intrepid Check engine light codes

I own a 1997 intrepid that recently had the transmission repaired. Shortly after the repair, the check engine light came on. I disconnected the battery to reset the computer but the light came back on again a few days later. I did the "on/off" sequence to determine the error codes and the flashes/pauses indicated the codes are "12" and "21" in that order. The car seems to run ok so I don't think it can be anything too major. Can you tell me what these codes mean so I can get the needed repairs...

Thanks!