Need emissions help with '14 Pathfinder

[i6pwr]

Friends car, has 120K miles, runs perfect.

P0420 popped up and I don't recall a bank#..sorry this code has been here for a few months I believe.

They were told shop wants to replace one cat, but in my days of a shade tree diagnostician.....I would want to check sensors first.

So I hooked up my Torque Pro and being my first Nissan I had to check O2 sensors and cats, it looks to have AFR's for upstream and standard O2 for downstream.

There is no odors from the exhaust, no hint of fuel.

If I went on this graph alone, it looks like both cats are not working, but at idle both down stream cats are linear like it should be.

Does Nissan have that accurate of an idle control with the AFR sensors to maintain a steady flow of fuel to keep the cats happy?


Here's a shot when I blipped the throttle at idle with the engine warming up for about 5 min.

This is driving at about 30 MPH

What is suspect is the temps being exactly the same and the cat temp display was one for each bank, not the same bank.

Help me understand this, I can't see how both cats are toast. The graph shows both cats are doing nothing, but I'm skeptical.

Edit to add, the temps are sensor 1, so that can't be aft.

 

[Bailes1992]

P0420 is bank 1.

I always thought O2 sensors provided readings via a sensor range of 0.01 (lean) and 0.98 (rich) so I don't understand why the upstream sensors are providing values of 8v?

 

[FowVay]

It looks like the upstream sensors are becoming unresponsive after they get hot. Unfortunately they're a tad bit pricey to just throw at the problem. But, that's where I'd start my investigation.

 

[i6pwr]

I don't believe tbe upstream sensors are O2, sensors....but an AFR sensor...lambda.

 

[Trav]

A standard O2 and wide band (AKA AFR sensor) O2 are both Lambdasonde (AKA Lambda). It cant hurt to swap the AFR, if it does require a cat the AFR and rear O2 should be changed anyway.

 

[Chris142]

Fix any other codes first and see if 420 goes away too.

 

[i6pwr]

Only code was P0420.

I've had these pop up before on other vehicles, pretty much a cat performance code...cleared them out, and never saw them again for years, if at all.

I did reach out to someone and he said the downstream will have a slight sawtooth instead of a ruler line....maybe the PCM is seeing the larger sawtooth of bank 1 and is beyond threshold.

I'll have to get it on the highway and see how it does, wasn't able to shoot the temp of the cats yet.

I'm used to rapid sawtooth on sensor 1, and flat line on sensor 2 when working properly.

The exhaust plumbing at the cats looks to be a bear on this also.

 

[WeyounDS9]

You do not want to defer catalytic converter replacement.
All engines have some backpressure modern designs have more than others.

If the cat disintegrates it will suck ceramic particles into your combustions chambers.
Your VQ35de is an almost bulletproof engine, but only almost and external events like this could kill it (as they could any other engine)

 

[Trav]

That happens mostly with manifold mounted cats like on the Nissan 2.5

 

[Bailes1992]

Well I've certainly learned something new today!

Looking at those graphs again then. The 'ups and downs' of the bank 1 sensor seem to be far wider and more aggressive than the bank 2 sensor. Lazy sensor?

 

[JTK]

The upstreams are on the manifold and the downstreams are right on the outlet of the CC assemblies.

I can't really tell from the above data, but for sure there's no manifold leak, etc on the suspect bank?

The exhaust systems are stupid complex and expensive on 2013+ Pathfinders. It's like $2500 worth of parts just for the cat-back system. Add another ~$750 each for CCs.

 

[slacktide_bitog]

P0420 by itself almost always means you need a new cat. You should also replace all oxygen sensors along with it. Eastern makes good cats. For the AFR/oxygen sensors, get Denso or NTK

 

[Bailes1992]

Just did a little googling to broaden my horizons a little. I read in numerous places that the downstream/post-cat O2 sensor should be sitting around 0.5 to 0.7v. The bank 2 sensor seems to be doing this perfectly. The bank 1 sensor is running either side of this by quite a bit.

I'd swap the sensors from side to side first, if the fault swaps to bank 2 then you know you have a lazy sensor. If the fault stays at bank 1 then I'd be confident in condemming the CAT.

 

[i6pwr]

Just did a little googling to broaden my horizons a little. I read in numerous places that the downstream/post-cat O2 sensor should be sitting around 0.5 to 0.7v. The bank 2 sensor seems to be doing this perfectly. The bank 1 sensor is running either side of this by quite a bit.

I'd swap the sensors from side to side first, if the fault swaps to bank 2 then you know you have a lazy sensor. If the fault stays at bank 1 then I'd be confident in condemming the CAT.

Generally the downstream is almost ruler flat when the cat is lit off, or maybe a very slight sawtooth. Cat 2 IMO even looks slightly aggressive but I don't know what Nissan seems as acceptable.

Wouldn't hurt to replace both downstream sensors first, then if that doesn't fix it, replace the cat using the new sensor.