Code P1494 & P1684

P1684 is for the battery I hear.

But code P1484 - Incorrect input state detected for te leak detection pump (LDP) pressure switch.

These codes are according to my OBD II jeep codes, so they might be different for neons. I know that P0??? are all the same for all vehicles and codes starting with the #1 (P1??) are manufacture specific, but jeep and dodge are both part of chrysler so I assume they would be the same.

P1494 - Leak Detection Pump Sw or Mechanical Incorrect input state detected for the Leak Detection or Fault Pump (LDP) pressure switch.

First make sure your gas cap is on correctly. If it isn't, it can trigger this code. Secondly, I would make sure that all the vacuum routings in your engine bay are connected soundly. In particular there is a vacuum line that runs from near the throttle body, around the edge of the airbox, towards the firewall and then down into some emissions control equipment. Make sure that the line is not kinked, clogged, or disconnected. The pump itself is underneath, back behind the gas tank. It has one electrical connection and several vaccuum lines running to it so be sure to check them all.