When the light came back on, are you sure it isn't for another part of the system? Was the code cleared out after the valve was replaced? I am going to refer you over to here
Allpar has Dodge, Chrysler, Plymouth, and Jeep car, minivan, and truck information and you can look at the various tricks for dealing with Chrysler products. But my sense about your high mileage car is it's due for a tune up, O2 sensor replacement and a catalyst backpressure check just to get it back proper again.