LEFT REAR READS "XXX" . WHEN YOU START THE CAR MESSAGE BOARD READS "SERVICE TIRE MONITOR" . JUST REPLACED REAR TIRES AND REPLACED LEFT REAR SENSOR. . DO I JUST NEED TO REPROGRAM IT? HOW DO I DO THAT?

You need a pretty strong magnet(an old speaker mag will do) and enter into the TPS programming mode in your DIC. It will tell you LF 1st. place magnet over stem until horn honks then rf etc..

Click here for the full procedure.

Do me a favor, set up a video camera and record it so we can all see how high you jump whe the first horn beep goes off (it gets me every time)