help with some P0420/430 cat codes

The Gas and Diesel Engines - VQ40De, VK56DE, YD25DDTi, V9X, Transmission, Transfer Case, Oil, Differentials, Axles, Exhaust...

Moderator: volvite

the ocho
Posts: 27
Joined: Mon Oct 30, 2017 8:59 am

help with some P0420/430 cat codes

Postby the ocho » Mon Sep 20, 2021 6:57 am

So i've replaced my old 250k+ mile cats, also replaced all 4 sensors (those pre and post cat).

I'm still popping codes, but it's a pretty repeatable pattern. If the car is cold - it'll throw a code within the first mile. If the car is moderately warm (like after starting up after eating lunch on a long road trip) it'll throw a code usually within the first 10 miles.

if i reset the codes and blank out the learned map after warm up, it won't throw a code. I've gone 300 miles on a road trip and the pathy was awesome, had tons of power (I was towing) and felt awesome. As soon as we stopped for gas and lunch, then got back on the road it throws the code.


my only thoughts - something with the EGR system? Anyone have any insight into the issue??


silverarrow27
Posts: 414
Joined: Sat May 02, 2020 1:40 am
Location: Banning, CA

Re: help with some P0420/430 cat codes

Postby silverarrow27 » Mon Sep 20, 2021 11:02 pm

I'm not sure if Nissan changed anything on their ECUs, but in order for the code to clear by itself I needed to drive my 2002 Frontier for like 2-3 months before the code cleared itself.

TooMuchControl
Posts: 335
Joined: Tue Apr 28, 2020 4:41 pm

Re: help with some P0420/430 cat codes

Postby TooMuchControl » Tue Sep 21, 2021 4:01 pm

You didn't state how many miles you have driven since you've performed these changeouts.
By the looks of it, you've driven quite a bit and the problem persists....

Did you install the cats yourself, or did you have a trusty shop do this?
Are you always getting both codes?

What type of A/F sensors did you purchase? Bosch type?
If you have the old original ones, they probably aren't bad.

What's very odd is that you are getting both the Bank 1 and Bank 2 codes...I can think of these:

1) pre-existing condition that caused the old CATs to fail. Intake vacuum leak, leaking injectors. exhaust manifolds are cracked and leaking.
2) poor installation of the new CATS (leaking at connections, no proper gaskets installed)
3) A/F sensors or O2 sensors have failed, or do not respond.
4) both new CATs are bad.

I believe that the codes will only come on, after a certain number of "restarts" of the truck. So it makes sense that it throws the code when you start it up on a set number of restarts (it might have been the 5th time, just as an example). The codes will be sitting in the CPU buffer as a pending code, even when you have no "CEL".

Seeing that you know the codes, you have an OBDII scanner...
...see what the A/F sensors are doing. B1S1 B2S1. They should be moving.
One should be .6v, the other .3v I think.
If they are responding correctly, check your O2 and see if they are working.

The worst thing that can happen, if you have a pre-condition that caused your other Cats to fail, if you continue to drive it, you may actually foul your new cats and have to do this all over again in a couple of months.

For me, I'd take the car to the dealer and have them check.


Oh..just a silly thought. All the sensors are plugged back in right? I just wonder if someone forgot to plug everything back in, after removal....

OBDII scan will tell you right away....

Sorry for the open thoughts. There are so many variables....these are the ones I can think of.

TooMuchControl
Posts: 335
Joined: Tue Apr 28, 2020 4:41 pm

Re: help with some P0420/430 cat codes

Postby TooMuchControl » Tue Sep 21, 2021 4:08 pm

As for the reset of codes.

For me, it took about 350km of driving. I chose not to reset the codes when I replaced mine, to make sure the codes would clear by themselves. They did.

For certain, it reset by itself in less than a tank of gas of driving.

the ocho
Posts: 27
Joined: Mon Oct 30, 2017 8:59 am

Re: help with some P0420/430 cat codes

Postby the ocho » Fri Oct 08, 2021 2:45 pm

I have a suspicion that maybe some of the bolts on the cat are loose leading to a small leak.

I'm able to log using my NDSII app and can see on the "AF Alpha" channel a larger than expected difference between the b1 and b2 readings, usually when coming off throttle.

I'll have to dig into it more - the cats aren't in the easiest place to inspect :x


Return to “R51 Engine, Driveline and Powertrain”