P0420 code again
 

I have a 2004 TL, automatic. I have replaced all the o2 sensors. Spark plugs and coils are good. No performance issues at all. But, yet I keep getting the code ,,p420 catalyst below efficiency bank 1. All catalytic converters and exhaust pipes look in good shape..

What do I do ? And how hard is it to remove both cats myself? I'm somewhat mechanically inclined. .

Thank you...

Sometimes a reflash at the dealer can fix it.

If the precats are bad and you don't have to worry about emission testing, you can go with precat deletes or if you do need to keep the cats, there are vendors here who have high flow cats. Or maybe some members here who've swapped their OEM cats for high flow or deletes will offer them up for sale.

Front one isn't too bad to remove, the one on the firewall side is definitely tougher to get to. Access to a lift, long extensions, lots of penetrating oil would help.

Thank you ... I just put in an o2 sensor extender today. Let's see what happens now .....

Pull the power from the battery for an hour and fire her back up. I've had this show up three times as a false positive in my 204k miles of motoring...

this is almost always caused by a bad cat not anything else. every car ive had that this code came up needed a cat (at least 10x... i was buying and flipping auction cars for a while). a defouler on the secondary O2 should fix it, but if the cat is actually clogged then its not a good idea to do that. will need replacement, and you cant tell by looking at it... it degrades internally.

btw bank 1 is the rear bank, so i hope you put the extender on the 2nd O2 on the rear bank...

might need an ECU update from the dealership to correct this

I don't follow. Care to clarify?

like the others have said, 420 is set for cat. nothing else. replace it to correct the problem.

Unfortunately, Acura dealer doesn't have any pcm updates with false interpreted p0420/430 issues. No update exists for this type of a problem on any of their models.

The only vehicle I have seen this issue where a 420 kept coming back on after oe cat install was a Toyota Sienna, dealer did have a software update which fixed the issue.

these numbers always throw me off. had a similar error code tied to the emissions system, that would show up in the cold weather. dealership updated the ecu to correct it.

there have been ecu mapping updates that have helped eliminate some emissions codes.. but that would only be the case if something wasnt actually wrong anyway

Either cats or you have false positives from low amperage.. I had these codes thrown at me from battery and alternator failing.
A clogged cat would probably cause misfires as well.. start with the battery and alternator.

so is this the one by the firewall?

P0420 is indeed for the one by the firewall.

I have an on and off p0420 for the past 4 years. I didn't bother with it.