Is my catalytic convertor shot?

[lk777]

Hi all,

2011 Nissan Rogue AWD 157,000 miles

Recently I started to get that lovely P0420 code.

This is my Torque screenshot:


At 2000 rpm with the normal engine temperature.

O2B1 S1 is a wideband sensor, I believe.

Is this cat shot?

[VStar650CL]

That looks shot. The ECM isn't looking at voltages when it diagnoses a P0420, voltages are reserved for checking the health of the sensor. In diagnosing the cat, it's looking at switching time. The little ripples you see in the A/F (you're correct that it's wideband) are the ECM deliberately riching and leaning the mixture slightly to see how the rear O2 behaves. With a healthy cat, the swings in the rear O2 lag significantly behind the A/F. The amount of lag indicates the health of the cat, lots of lag indicates good oxygen storage capacity. For a completely dead cat the ripples in the A/F and swings in the O2 will track almost one for one. You can see that's pretty much the case with your ride, so unless you have a leak someplace in the vicinity of the rear O2 that's fooling the sensor, that cat is dead.

[lk777]

I made that decision based on the multiple YouTube videos. My initial test was done in parking with 2000 rpm. This is how those geniuses tested their CATs.
But today I decided to make a 50-mile highway trip with the continuous Torque real time monitoring.
This is what I got today:

and


It looks fine to me.

This is how understand it. Correct me if I am wrong.

When a car under the normal load with the hot enough cat, with the right AFR, a cat works as it is supposed to work - no O2 in the outlet, it was used by the catalytic to do its job.
When a car in park with the minimum load on the engine and the cat temp is low, it has nothing to burn in the cat, excessive O2 is coming out of the cat outlet (it doesn't matter how the engine is hot).

I made 100 miles after clearing P0420 and no code so far.

I realize that this cat is quite old. Considering that lately I used this car only for the city driving with frequent start/stops, I think that the ECM detected some abnormality.
I always used top-tier fuel and it doesn't burn oil. Will continue to drive it on highways occasionally to make the ECM happy.

[PowerslavePA]

P0420 is a downstream code, which means the CAT is not performing
like it should. It is an efficiency code, but not a clogging code,
just the opposite. IT will not effect fuel miles per gallon. I ran with
P0420 and P0430 for over three years with my Camaro.

Downstream means after the primary cat.

Sometimes an O2 spacer will fix the issue, it did with mine till I
gutted the primary cats.

[VStar650CL]

P0420 is a downstream code, which means the CAT is not performing
like it should. It is an efficiency code, but not a clogging code,
just the opposite. IT will not effect fuel miles per gallon. I ran with
P0420 and P0430 for over three years with my Camaro.

Downstream means after the primary cat.

Sometimes an O2 spacer will fix the issue, it did with mine till I
gutted the primary cats.

You have to be reeeeeally cautious about P0420/P0430 on QR's or VK's, both are prone to inhaling a cat if it gets bad enough to melt. The engine is toast if that happens. VQ's are a lot less susceptible, although it isn't unheard of. P0420/P0430 is your early warning system and spacers disable it.

[PowerslavePA]

Those codes are monitoring codes ONLY. All the P0420 code means is
the Catalyst is no longer doing its job properly. This code is set when
the downstream sensor has the same readings as the upstream sensor.
SO, that means it sees the same gases the upstream sees, which is
before the CAT.

A clogged cat may get hot enough melt, but this is the exact opposite of
clogging. This code means it's more free-flowing.

I think what you REALLY need to say, is because the CAT is so close to
the head, right on the exhaust manifold, that if it breaks up, it can get
into the cylinders, but still has to get passed the exhaust valves.
You're also talking worst case scenario, because they don't break apart
under normal circumstances.

The Cats on my Camaro were right at the flange on the manifolds, and
the driver side deteriorated and nothing got into the engine. The
secondary cat was also gone. So, I had to gut the passenger side to
match.

[VStar650CL]

That's all true, but healthy cats don't melt (or even crumble). I don't think I've ever seen an inhaled cat that didn't give plenty of warning that it was dead, and I've seen plenty of inhalation deaths. It isn't really proximity to the head, it's that Nissan uses some pretty severe Miller-cycling on most of their engines to avoid the need for an EGR Valve. If the cat crumbles it doesn't hurt anything, but if it melts you get molten particles being sucked back into the exhaust valves by the Millering. The particles are at welding temperatures, so the result is catastrophic. This is what happens (QR25 shown):

P0420/P0430 is generally the only warning you'll get.

[VStar650CL]

PS - Note the exhaust valve on the right welded open a bit. That's typical, and it's why the volume of molten crap inhaled can be so large. Once a valve is stuck, you get genuine suction on the power stroke instead of just Miller backflow.

[PowerslavePA]

P0420 code, will not overheat cats, because that means they're flowing
too freely, and not catalyzing properly. CLOGGED cats, will overheat,
and you will not get a P0420 code for that. You will get another
code indicating voltage is too high, because the O2 sensor is running
hotter than normal. That would be P0138 for the downstream, or
P0132 for the upstream. That is when you want to pay attention to
what's going on with the CAT.

EGR was abandoned for many reasons. Most direct injection engines didn't
have them. Dodge, on the other hand, brought it back on their 3.6 Pentastar
to squeeze another MPG or so out of it, as the earlier ones didn't have one.
My Camaro didn't have an EGR on it either. My V6 Mustang does, but the same
year range V8s do not, and they are not DI engines. Most port injected
engines have EGR because they're not as efficient as the DI engine. Every
DI engine car I have owned, did not have an EGR, with the exception of my
2013 Jetta Diesel, but the EGR on a diesel doesn't work the same way as
it does for a gas engine.

[VStar650CL]

P0420 code, will not overheat cats, because that means they're flowing
too freely, and not catalyzing properly. CLOGGED cats, will overheat,
and you will not get a P0420 code for that.

Nobody said P0420/P0430 indicates an overheat. It indicates a dying cat, but dying cats are always at risk of crumbling or melting. By the time one does and you get some other code, it may be too late. P0420/P0430 is generally the only advance warning you'll get.

EGR was abandoned for many reasons.

Sadly, it hasn't been abandoned. Some of the newer Nissans like the gen3 Rogue are going back to it (ugh).

[PowerslavePA]

EGR has been abandoned for some. Like I said, Dodge brought it back, and
as you said Nissan. However, starting with the 5th gen Camaro, they
do not have one V6 or V8, and still do not have one. V8 Mustang doesn't
have them anymore, since 2005. Some carmakers have indeed abandoned
the EGR. Some Subaru models no longer have an EGR.

I actually lost 2MPGs when I deleted mine on the Mustang. I hooked
it back up. Gained with the diesel I had.