Code P0420 and Dealership Recommending $2500 Repair!

Yes, I suggest you seek a second opinion. So far it sounds like the catalytic converter needs to be replaced, worst case. Best case, maybe if you just replace the air/fuel ratio sensor upstream from the cc, the DTC might go away.

 

In most of these cases for P0420, it is safest to replace both O2 sensors and the cat converter -- with the cheapest parts available. This is several hundred dollars, but is guaranteed to fix the problem. This advice does not apply to California residents (who get 10 year, 150K mile warranty). If you are in California, then this would explain the criminally negligent repair estimate.

Having P0420 come and go is VERY COMMON for a failing cat converter.

 

Thank you for the post. Going through this now with my '06 346K miles. Dealer wants to replace the Cat Converter, $2200 in Nashville.

 

They're (the dealer) not referring to the cat converter, they're referring to a charcoal canister that's associated with the fuel delivery system.

Here's my advice; ABSOLUTELY do not let the dealer replace this for $2500. None of this makes sense. I'm betting what probably happened is you didn't screw the gas cap on tight (causing the CEL). The dealer didn't know what to do but found a 0420 code stored in the ECU and jumped on that. I would wait for the CEL to come on and stay on. If it doesn't, you have no problem. If it does and you're consistently getting a 0420 code, refer to Seilerts advice. I'm betting you don't have any problem except not screwing the gas cap on tight. I could be wrong though and that's why we wait to see if the CEL light comes back on consistently.

 

Wow, 346K miles? Have you posted in the 299,999 mile club yet?

Eastern Catalytics makes a 49 state legal bolt-right-up converter for 2004-2009 Prius for $350 or so. You can also get about $50 from a scrap yard for the old one.

Bottom line on catalytic converters:
If you do not live in an inspection state, and it is not illegal to do so in your state, and you just don't care about emissions or having the CEL on, cut the converter out (they can clog) and just have a muffler.
If you do not live in California but are subject to inspection, get aftermarket equipment.
If you live in California and have less than 150,000 miles, it is covered by warranty.
If you live in California and have more than 150,000 miles, then you must use OEM equipment for any repair made locally. It is not clear the legality of driving to a different state and having aftermarket equipment installed.

 

What range bump in emissions would accompany each choice ?

 

forget i said anything.

 

I apologize for being a little too flip. I have corrected my post accordingly.

 

Without a cat, it is probably still better than the Monte Carlo lowriders that we have in our neighborhood. I don't know the difference between factory and aftermarket but I suspect it is minimal.

 

I believe the major difference between factory and 49-state aftermarket is that the likely service lifetime of the latter is short. Catalytic converters certified for CA sale must have a 5 year/50K mile warranty, and that period is less than half the expected lifetime of the factory part.
Aftermarket Catalytic Converters

 

Absolutely, the aftermarket has a shorter life expectancy. I was addressing the emissions converter efficiency, which I suspect is minimal, since aftermarket units have to pass EPA performance tests.

 

P0420 is the result of a self test that fails. The down stream O2 sensor has too much flucuation when the mixture is run rich and lean. I didn't figure out the correct value, but is seems that if you get the wire where the sensor enters the computer, and put a nice size electolytic capacitor there, + lead, negative to ground of 1000 ufd 10 volts or so, should smooth it out and the light should stay off.
I have getting getting the DTC, periodically, but now with the cooler weather, it has been off for over a week.
I understand that the test is overly sensitive, and the emmisions are probably still within spec, but higher then before.
Of course, with 350K the CAT is gone. If you plan on keeping the car another 350K, change it and he sensors.
Don't go to the dealer, go to a muffler shop.