Had code P0420 below threshold bank 2. Replaced cat bank 2. 1 week later got the same code. Mechanic replaced cat again and 2 O2 sensors. 1 week later got code P0202. Replaced fuel injector. Now 4 days later getting P0420 code again. I have already put a big chunk of money into this....any thoughts?

 

What engine size do u have?

 

6 automatic

 

ok did u guys look up a 420 its bank one not bank 2 the head that has #1 cyl is bank one

 

Maybe so, but the #2 bank cat is a lot easier to work on. ;-)

 

i may have the code # wrong, but it was definitely bank 2, just checked it again last night at autozone. It's been 48 hours since the check engine light came on and this afternoon it has gone off.

 

and tonight the check engine light is on again, went and had it checked and it is bank 2 p0430 code.

 

Check for exhaust leaks around that cat.
Have you been getting smoke out the exhaust? If so, you might have an oil leak in the engine that's contaminating the cat.
Did the mechanic install a brand new cat or a used one?
You might need to get a better scanner hooked up to look at some freeze-frame data to help track this thing down.

 

much testing done,
no leaks around cat, no smoke from exhaust. Replaced all 4 o2 sensors now and its responding well....only time will tell...thanks for the input!

 

I don't have Alldata in front of me, but a few things that come to me are, as was stated earlier P0420 is bank 1 cat efficiency, so make sure the correct cat was replaced. Are they positive there's no exhaust leak? Possibly in the flex pipe/manifold? The way I test that usually is stick a rag in the tail pipe to create more back pressure and see if I can hear or feel an exhaust leak. Second, since these issues seem to be popping up sporadically have they hooked up a more in-depth OBD II scanner to the vehicle? Something like Snap-on's Veerus (which we used when I worked in a shop) gives a knowledgable tech a whole lot more information then just a code. Did you use an after-market cat with this as well or did you go OEM? Some cars, especially Sebrings are very particular with that and I've seen issues arise when using a Walker, Bosol, etc... cat. I hate to send dealers money, since there prices are usually astronomical compared to the aftermarket options (which are often times better quality then OEM) but with cats I play it safe, it's a serious investment on an item that cannot be returned and is essentially worthless once it's been installed (only thing you can do is either exchange it for a new one or sell it to a scrap yard for ~$100).

Also, Since the injector code popped on during all this and the code is jumping around and changing every time I would possibly think a faulty ECM or even a batter wire in the ECM can be causing it as well. I would check the leads to the O2 sensors, and make sure there's no damage to the wiring to the ECM (pull the connector and make sure it's in good shape too). Worst case scenario take it to a dealer, bite the bullet and pay the diag (which will cost a good bit of money), and see what they say.

These are just a few thoughts I had off the top of my head.