Nissan Repair: odb2 error 0420, fuel pressure gauge, nissan pathfinder

Question
QUESTION: Catalyst System Efficiency Below Threshold(Bank 1), any suggestion on fix and what to fix?
Thanks for previous answer on my electric window, works great!!

ANSWER: David,

This code means that the converter is unable to do its job.  That is, the converter is either contaminated with gas or oil blowby or the injectors are feeding too much gas or the sparkplugs are unable to ignite the fuel mixture sufficient to allow the converter to burn the fuel off.  I would start by getting a tuneup and then checking the fuel pressure.  Also, if the engine is consuming oil this can kill a converter.  Switch to Mobil 1 5W30 for starters and if a tuneup and the oil change does not do the trick note what the fuel pressure is doing.  A stuck injector can over fuel the converter where it will melt and then have to be replaced.

---------- FOLLOW-UP ----------

QUESTION: Did a tune up, no change.  How do I cheeck out the converter?  Are there any other symptons like bad gas miles?  I burn about 1/2 quart oil per 3000 mile.  No leaks found anywhere.  I also am only getting 17.5mpg highway, 2002 Nissan Pathfinder LE.  Once again thanks for all the feedback!!!!!

Answer
David,

First, I would check the injectors to see that any are leaking. If you have pulled the plugs figure out which hole they came from and look for black and wet ones.  Those are the ones with the leaky injectors.  That is, they are not sealing off when they should.  A leakdown test with a fuel pressure gauge would show if the pressure drops off when the vehicle turns off.  The pressure should stay for 30 seconds or more.  If ti leaks right off you have a defective injector.  Nissan was bought by Renault a few years back and now you never know if you are getting good Nippondenso injectors.  Bosch has entered the parts stream and those are known to have problems in Nissan cars...