Hey....I just bought a used montero and I have two failure codes. P0420-cat efficiency fail and P0442 evap system-small leak code. Is it possible just an 02 sensor for the P0420 code?? Any suggestions?? I am trying to just basically have a friend do it for me because I dont feel like getting screwed over by my uncle who is a mechanic and screws family members out of money.

 

no, its not an O2 sensor. You have a failed cat.

and the evap leak is likely from a gas cap.

 

P0420 is the bank one cat conveter which failed.

The p0442 you could try throwing a gas cap and see if that fixes it.

After you do any work to the car disconnect the battery to erase the check engine light and drive it to see if the same codes come back on.

 

+1 on the failed cat. Been through this twice on my '99. (190K miles)

As detailed here: http://www.fordscorpio.co.uk/catmonitor.htm the OBD II program goes through a sequence and will not even run the cat test unless & until it gets the proper signals from the O2 sensors. (scroll down to the section on DTC's if you want to skip the science lesson) So the fact that you're seeing only this code means your O2 sensors are OK.

Ron

 

I've got the same 0442 code, but mine is probably the tank. It leaks fuel on the ground when completely topped off and up the filler neck a little. Going to fix it now that its warmer. I'll take pics.