Recommendations for a cat

Have you already checked for exhaust gas leakage and inspected the air/fuel ratio sensor, the oxygen sensor, and their wiring, as described in the Repair Manual procedure for P0420?

If so, and the trouble persists, the textbook answer is to replace the entire Front Exhaust Pipe Assembly, Toyota part number 17410-21500, which includes the catalytic converter. The list price is $1957.91, but one Toyota dealer near me offers them on its website for $1450 or so. The gaskets at its two ends are non-reusable parts, so you’ll need those, too, as shown in Figure 17-02 of the Electronic Parts Catalog.

I’ll let those with experience in this area comment on alternatives.

 

How much oil does your Prius consume?

Only way that catalytic converter can affect fuel economy is by being clogged or badly restricted. Most common reason (on all cars) for catalytic converter to become clogged is oil burning engine. But catalytic converter can fail and became clogged for different reasons as well. You should really know why it failed before replacing it.

 

+1.

With those miles I'd consider a $1000 worth of parts to be very non-trivial, and besides you may just need to clean or replace the O2 sensor(s).

As mentioned above n addition to oil use, you need to examine your fuel efficiency.
If yours is unchanged, then one would presume that the cat is not restricted.
Since you don't live in Caly, and since Western Oregon is probably a Prius dense area in addition to having lotsa 4x4's you may need to get some quotes from the pros - meaning some one of the designer exhaust shops in Portland.
Catalytic converters are not emerging technology, and people who live on free soil can usually get them replaced for just a few hundred bucks.

Finally.....since you live in an area where a VET is an expensive place to take a car, in addition to an expensive way to scare the crap out of your cat (the other kind) I'm presuming that your car passed the last Vehicle Emissions Test....which also points away from a failing cat.

Good Luck!

 

The cat(s)/02 sensor issues can be a symptom of high oil use in older, high mileage engines. Personally, I would go the used route installed at a muffler shop for the least $$$. If you're still on the original HV battery, you also have bigger issues coming.

 

I recommend a Bermese Mountain Cat. They have a loving and subdued personality...Sorry

I'm not sure why others are saying you need to replace a $1400 part. First, I would figure out if the problem is the cat or the oxygen sensor. There are tutorials online and there's nothing special about a Prius really in this regard. Most typical on Prius' over 200k is bad cats, often from burning oil, so I think your O2 sensor is likely okay.

If it's the cat: Look on Amazon for a compatible one:

Before you buy, call your local muffler shop and confirm if they'll install it for you. In Colorado, this works, but as Oregon is a CARB state, they may be restricted from fixing the car without a factory cat. If they can install it, buy it and take it to your local muffler shop and get it installed for $150-200. Any muffler shop worth their snuff will have an OBD tool and can do the analysis to determine if it's the O2 sensor or bad cat. It does not need to be an exact fit, just enough of one that they can weld it in.

One other fix that sometimes works for cats is to run a gallon of lacquer thinner with a tank of gas. This only works for cats that are marginally bad, and basically works by cleaning them out. However lacquer thinner is not good for the fuel system, so it has a little bit of risk, and if you do it, should burn through that tank of gas within a couple of days - don't leave it in there for a month.

 

Does this take into account the small volume of the Prius' fuel tank, compared to other cars, and the presence of the bladder?

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Haha, there's definitely not engineering analysis that can be found for doing this - just a mechanic's trick for old cars that don't have too much value (and therefore the risk to the fuel system is acceptable). Lacquer thinner is definitely not good for the bladder. I agree half or 3/4 of a gallon might be better.

 

It sounds like this will work great! Only thing I would add is to confirm this won't cause a problem when it comes to your emissions inspection. In Colorado on the Prius they just do a OBD check and quick look under the car to confirm the exhaust isn't leaking. However in California I believe it's illegal to use aftermarket cats. No idea for Oregon - so I'd confirm this before replacing.

 

Ok, I just did all that. Replacing the upper A/F sensor is going to be pretty hard (it is in a metal shield, and also needs special tool, and is in hard to reach place), and it may never go bad. If the ECU is showing cat codes, they need to be replaced in a set. I bought the whole pipe and 2 cat assembly for about $150-$200, I think. just search ebay for prius catalytic and check that it matches your model and year. it is actually fairly easy to replace, just make sure you cut out your exhaust pipe in the right place and fit the upper gasket well so it doesnt leak. The o2 sensor is probably ok, if not, they are cheap. You can also try cleaning them.
You should be able to check the A/F 3.3V sensor and also fuel trim using torque.
I am pretty sure California and maybe New York are the only states one needs to worry about extra regulations.

 

No, no it is not responsible for your poor FE and likely no the cause of the P0420 (cat efficiency) code you are likely getting.

Aftermarket cats are universally CRAP, if you like changing them, go for it; but that's not your problem. The most likely cause(s) are: Exhaust leak, failed Wide-band Oxygen sensor (WBO2), wear of the cat that is enough for the ECM to detect (Toyota and Subaru are KNOWN for this), but that still performs just fine in terms of emissions and lastly excessive oil consumption that has damaged the cat.

 

If catalytic converter is badly restricted it can affect fuel economy.

If catalytic converter is working just below the threshold and tripping the P0420 you can use something like O2 sensor extender to keep the code away. You can do that bough with old factory catalytic converter or with new(er) aftermarket one.

 

Nope. The MAF and WBHEGO control FE, if the engine cannot breath less air and therefore correspondingly less fuel is injected.

 

It’s not that simple.

Yes Prius engine isn’t a MAP based engine where restricted exhaust will cause rich running. But increasing the pressure in exhaust will reduce engine efficiency. Prius engine normally operates with relatively high throttle open and high load situation. Where added exhaust pressure will cause bigger drop in fuel economy compared to normal car with same amount of restriction.

And exhaust can be very badly restricted in some rare cases. If exhaust would be so badly restricted that engine power wouldn’t be enough to accelerate normally hybrid system would basically use battery power most the time causing engine to be run all the time trying to charging the battery back up. This would of course ruin the fuel economy.

 

I get what you are saying in terms of the energy it takes to push the restricted exhaust out, but if the pressure were high enough to be a problem, the EGR system would be overcome with exhaust flow and the engine would simply die as it cannot run on exhaust. EGR flow is highest at light load (steady-state highway typically) and you would also get MAF codes that indicated airflow below the look-up table values as the higher EGR flow will provide a 1:1 offset for intake air.

Even minor exhaust restrictions often manifest as serious system leaks before any performance loss is noticed.

 

I was really talking more in general and not on this exact situation.

But I’m not sure that it would stall the engine (if restriction is bad but not too bad) as ECU can just control cam timing to increase power and degrease EGR flow. Gen 2 Prius doesn’t have separate EGR valve and can only have limited amount of EGR with cam timing. But off course bad enough restriction would cause fault codes like you said.

There has to be an area where the restriction is bad enough to effect fuel economy but not bad enough to cause it not to run at all.