2001 QX4 Catalytic converter questions

[jebbis]

First time poster. I have been a lurker for a few years now and have found a plethora of great info here.

My 2001 QX4 is throwing both P0420 and P0430. I know these are codes for both the left and right cats, but what I cannot figure out is if there is a way to positively determine if it is the cats or if it is the oxygen sensors or something else. Is it typical for both of them to go at the same time? Could this be indicative of some other issue?

I should add that P0160, O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2), showed up recently. It did not come back after clearing out all codes on a scanner, though. I have not checked it in the last two weeks, though.

I'd rather learn how to change them myself, if it is the cats, than pay someone else. The following thread is very helpful for this:

zer...erter

I know all of the aftermarket cats have less precious metals in them and therefore last longer. Are there any brands that are better than other or that people have had success with?

[abadlovesong]

i have the same issue. my '01 pathy is throwing out p0420 and p0430 . It was intermittent at first and now it stays on all the time. The only time it goes away, is when i take a long distance drive (which probably means its pretty gunked up inside and long, high speed driving helps clear it out some).

I've heard that there are 3 cats in the pathy. I'm not sure if its true, and need to know which one are the codes pointing to. I'd like to do the repair myself. But also concerned about using an aftermarket cat. I'm moving to california soon, and it is the only state in the US where you cannot use an aftermarket cat b/c of air quality laws. Whether that means they say you can't use an aftermarket one, or an aftermarket one won't pass a smog test. If its just the former, that'd be nice but i have a good idea that its the latter.

[jebbis]

I believe it is only 2 Cats.

http://www.nicoclub.com/FSM/QX4/2001%20QX4/

This engine control system doc explains codes P0420 and P0430.

The accelerator control, fuel and exhaust system doc has the schematics for catalytic converter into the pre muffler and muffler.

It does not really answer my questions but it is good info. I believe your pathy and my qx4 are exactly the same other than interior...

My issue is that we have emissions testing here in Chicago and of course mine just expired. The truck cannot pass the self diagnostic tests so even if the check engine light is not on, it fails the ODBC test at emissions.Any help is appreciated on the cat questions...

[alexf20c]

clearing a DTC will not automatically allow the vehicle to pass an OBDII inspection. by clearing the DTC, you set that circuit to Not Ready, which also counts as a test failure. to get the circuit to read Ready, you need to give the computer ample time to rerun the test - and pass.

the reason the code gets cleared after long driving is because that is when the computer runs the test - on no load driving (cruising) between 50 and 60mph.

P0420 and P0430 only indicate that both cats are below threshold. it does not specify which (if at all) O2 sensors are faulty, whether it's bank 1 or bank 2, or upstream or downstream.

the P0160 indicates a bad downstream sensor on bank 2. recheck your DTCs and see if it's there again. if it is, replace that sensor and see if P0430 goes away also.

[jebbis]

if it does not go away and the 430 still exists, would that indicate with any degree of certainty that that cat would need to be replaced?

[abadlovesong]

if it does not go away and the 430 still exists, would that indicate with any degree of certainty that that cat would need to be replaced?

Ok, i figured out my problem and the cause for the p0420 and p0430 codes. Someone mentioned on the forums about the first thing to go wrong with the exhaust system were the resonators that sit after both cats. If my memory serves me, it was pwnin' who mentioned it.

anyway, he mentioned that the housing starts to split and crack, and exhaust leaks out, causing a pressure drop in the exhaust system. So, i got down and checked mine and sure enough, both are split open. That's why bank 1 and 2 of the cat is 'below threshold'.

Might want to check yours as well. While i could just replace the resonators or remove them completely, i think i'm going to just replace the whole system.

[alexf20c]

that's incorrect. the upstream O2S measures oxygen pre-catalyst to help determine air/fuel ratio. the downstream O2S measures oxygen post-catalyst to determine whether or not the catalytic converter is actually working. neither could actually give a damn what happens after the downstream sensor, whether there's a crack in the resonator, you have a cutout before the resonator, or you're missing a muffler, or whatever.

[abadlovesong]

that's incorrect. the upstream O2S measures oxygen pre-catalyst to help determine air/fuel ratio. the downstream O2S measures oxygen post-catalyst to determine whether or not the catalytic converter is actually working. neither could actually give a damn what happens after the downstream sensor, whether there's a crack in the resonator, you have a cutout before the resonator, or you're missing a muffler, or whatever.

hmm, nevermind. guess that's gonna be a seperate issue..