Some 2007-08 Grand Cherokee and Commander SUVs with 5.7-liter engines may turn on the Check Engine light and store trouble code P0420 and/or P0430 in PCM memory.
Jeep says the problem typically affects trucks built before Jan. 8, 2008, and is most likely due to electrical interference affecting the signal of the post-cat O2 sensor(s). Reprogramming the PCM with updated software is the only reliable fix.
Check with a dealer for the specifics of the flash.