I have a 97 zj Jeep 5.2L with about 157,0XX miles.

I had bought the car about a year ago with 139,XXX miles and kept it will maintain since I have owned it since. I just had a CEL come on yesterday with a PO420 code, not sure if its a CAT or o2 sensor. I just cleared the code today after work and wanted to get some input on what I should be checking if it comes back on before I leave on a trip after new years.

Thanks for your help.
Kevin

 

bad gas?

 

There are various codes that could be given if it was the O2 sensor. They will trip codes for switching rate, circuit malfunctions etc. The P0420 simply put means you have a bad catalyst. I am sure you looked by now but the cat might not even be there. This code tends to pop up more often with highway type driving but YMMV. I would not let this code stop you from taking a trip though. Worst case scenario could be that the cat gets stopped up causing a loss of power. You might fit a "test pipe" in the cats place to check for restriction.

The conditions needed to set a P0420 basically would rule out a sensor failure. The reason being is for a catalyst efficiency code to set it means the rear O2 (catalyst monitor) is mirroring the values of the front O2 sensor. If the sensor was bad you would probably see values that did not change, low or high voltage or open circuits. The PCM knows the sensor is good, but it does not like what the sensor is reading indicating the catalyst is not cleaning the exhaust emissions.