Hey all,
I need some help here, or at the very least a direction to start moving in. For the last I'd say 3-5 months, I've had the P0420: Catalyst System Below Efficiency Threshold - Bank One code coming up, as will as the MIL on the dash. I should say that I have noticed no ill effects that would be indicative of a faulty cat. There is no stumbling, stalling, rough idle, power loss, etc.etc.etc. The car runs beautifully.

However, New York requires a annual inspection, and I'm about 3 weeks overdue for it. I have tried everything I know to get this fixed (repairs and fixes listed below). This past week I had it looked at in the h̶a̶c̶k̶ ̶s̶h̶o̶p̶ auto shop and not only were they unable to diagnose it, they even managed to produce a new code, a P0302 Cylinder 2 Misfire code. So I need some direction as to what my next step(s) should be considering that I now have a P0302 and P0420 code.

I should also note that the car was struck by lightening several years ago which caused a host of problems that was ultimately attributed to being a fragged ECM. Replacing the ECM cleared up all of the problems.

List of fixes:
-Replaced leaky flex pipe on exhaust line - no effect.
-Replaced downstream O2 sensor on Bank 1 - no effect.
-Ran injector cleaner through tank several times - no noticeable effect.
-Ran Cataclean through tank twice - Cleared P0420 code for about a day.

Thanks in advance for any advice or help.

 

what engine do you have and model sedan or coupe ,when was last time it was tuned up(plugs) ,I've seen a bad spark plug #1 cylinder cause a p0420 on a relatives car('99 ford contour) her car ran normal also ,did you check ground strap on exhaust its on back side of muffler

 

I had the same codes on my 06 SXT 2.7L. Turned out to be the front cat was almost completely plugged. It turned into custom headers and full exhaust, which not only solved the issue, but added power and economy as well.