Swapping the stock CAT for aftermarket?

There is no danger, but in CA there are no after-market catalytic converters for Prius that have been CARB certified, so anything other than the OEM catalytic converter is illegal.

 

^ That.

They can work just fine on a purely technical level, but it's radioactive-kryptonite-illegal in California. Most sellers won't even ship them to CA addresses; been sued by state agencies too many times.

So... if you plan to get rid of the car before its next smog appointment, go for it. Otherwise seek the real deal, it's your only practical repair option.

 

Are you in a San Fransisco that is not in California or New York?
If so, there is no trouble.

as an example:

 

Then you're committing fraud.

Your kids must be proud.

 

Since my 2008 Prius Tspirit had its catalytic converter ripped out in November 2018, I’ve been running with a reputable £150 non-OEM CAT in my vehicle. Nothing has failed. Indeed, this summer, I recorded the highest ever MPG from a full tank of fuel. 68.1 mpg / 641 miles (UK) - and that was out of 42.13 litres of fuel used - could have made 650 miles!!!
So, almost 2 years of running on a non-OEM cat, and nothing has failed.


iPhone 6s +

 

Well, I can't make you any guarantees but maybe the manufacturer can. Seriously though, lots of aftermarket cats work great, last ages and don't throw codes, but some don't hold up.

Lots of non-California-based Prius owners have used them- I haven't kept track of which brands are best.

IIRC the part does not usually require welding to install unless the previous cat was removed with a saw, e.g. theft. In that case it may be necessary to get the pipe feeding into it or trailing out- we can't know where the thieves made the cuts.

 

Please let us know what make and model you end up using, and how it performs and holds up over time.

 

The biggest problem with cheap parts is well, they are cheap, and you often get what you pay for. Ignoring any state legalities for now, I often see aftermarket replacement cats not "holding up" on OBD2 cars. It might be a month, or it might be a year, but the check engine comes back on with a P0420 cat code. Think about it. the OE has precious metal inside to make it function- platinum, palladium, etc. If a replacement cat is much cheaper, it's because it has (much) less of those metals- and so it can't function as well or as long. There may be replacement cats that do ok, I just don't know of any.

If a car was sold in a state that required California emissions, then it usually needs a better grade of cat. The engine computer has stricter guidelines during its on board testing and a generic federal emissions cat will often fail.

Whatever you do, make sure that the replacement unit is installed without ANY exhaust leaks. Zero. Not even a pinhole. Even a tiny leak can throw off the on board testing and create a false failure. That usually requires someone with decent welding skills.

 

they don't live year-round in California

This pretty much says it all...I would do the same thing.

I have several Gen 2s in my family. They have ALL been swapped to aftermarket $125 converters from ebay. So far, no problems.

Recently, I purchased 3 more from ebay, but from a different vendor. Upon initial inspection, I liked that they had the same type flange as the OEM (even tho the photo in the auction shows a solid plate type flange) and they actually come with bolts that have the correct thread. They use a bolt with a spacer sleeve and new spring. Many others come with a smaller diameter thread that just slides through the OEM threaded holes and you have to figure out how to get a nut onto the back of it. That's a load of crap, and I made my own fastener system for those. I installed one of these (3) new ones in a friends car this weekend and hated it. The flange that bolts to the exhaust manifold was welded on at a different angle on all three pipes. I ended up installing and removing 6 times with different donut gaskets trying to get a combination that wouldn't leak. What was happening was the 'new' pipe had to be lifted a bit too much to slide over the cut end of the oem pipe, it was pulling the bottom of the flange away from the donut, so a huge leak would occur. The new pipe with a flange angle closest to the OEM finally worked. I think I can resolve this problem on the other two by putting some additional 'bend' in the section of pipe between the two converters to compensate for the 'off' angle of the flange.

2004-2009 Toyota Prius 1.5L Catalytic Converters Inc Gasket & Hardware 10H643044 | eBay

 

Some one entered San Fransisco as your location. Apparently this is wrong.

 

I didn't see where you said your current catalytic converter didn't work anymore. Is your car's check engine light on now? Does it need a new catalytic converter? Or are you just wanting to change it for the fun of it?

If you swap it out without having actual problems you could end up paying money for a lower quality cat than what it has now. Doing that would be throwing money out the window.

Personally I'm fed up with the terrible quality of aftermarkey parts. I'm sick of having to replace CV axles and wheel hubs annually, door handles that last a week, 12V batteries that work for only a couple years, etc. I'm sure there are perfectly good aftermarket parts out there. But for me, I always seem to get the bad ones so I now try to keep it as OEM as possible.

I just got my Prius and the previous owner said the cat was dying and the CEL did come on and did have the low cat efficiency code. Anytime I would reset the code it would come back on rather quickly. But after fixing the HV battery and filling up with Top Tier gasoline I haven't had the CEL come back on nor do I get any codes. If it does come back on I'll try cleaning the cat out first. If it's too far gone I'd be very tempted to go with an OEM cat over a much cheaper aftermarket one.

 

There are a large number of location dependent questions. (How long is my warranty, as another example)
We try to give the best answer for the location we see.