While driving my V6 4Runner on a highway trip with about 123000 miles on the vehicle, my check engine light and VSC light came on. I brought it to the dealer the next day. The dealer charged me $110 to check the code. They tell me the code PO430 means my catalytic converter is not working to efficiency and needs to be replaced. They estimate the repair at $1200. I then research online to find out more information about this code. I find out O2 the sensors may be failing from age and if they are unable to deliver the correct information to the ECM, it is possible to get a PO430 or PO420 code.

I bring it back to the dealer and have them check the sensors. Then they tell me, "the good news is your sensors are OK, but you actually need two catalytic converters." Again, I thank them for their time and take my 4Runner. I stop and pick up some Seafoam additive.

When I got home I disconnected the battery to clear the codes and added a can of Seafoam to the gas tank with a full tank of gas. I then added Seafoam into a vacuum line per the instructions. After that my 4Runner ran like it was brand new and the mileage increased 2 mpg on the highway. I purchased my own scan tool to check codes and after about another 2000 miles my check engine light came back on. I had the scanner with me on a trip when the CEL came on so I checked the codes. PO430 again. This time I cleared the codes with the scan tool. Everything came back to normal except a system monitor for the catalytic converter. My first thought was the dealer was right and this is going to be expensive. The scanner indicated "catalyst monitor incomplete". Some scanners might indicate this as "not ready". I didn't get any codes but went through plenty of drive cycles which should have reset the catalyst monitor. After 1500 miles of the monitor not resetting, I had to do something to pass my states emissions test which is done by OBD-II to verify there aren't any codes pending and all monitors are working OK. I bought two post-cat heated O2 sensors, installed them, and drove the car 4 miles and had all monitors functioning properly. The next day I passed my state emissions and safety inspection at the same dealer that told me I needed two catalytic converters.

I am sharing this to help others with a similar situation to understand that in this situation, the code indicated the catalytic converter was not working up to efficiency. But in reality, it was the O2 sensors malfunctioning, making the ECM think the catalytic converters were bad. With new sensors the ECM now gets an accurate reading and all systems are OK. I paid less than $75 for each sensor and I bought Denso, direct replacement (same as OEM in a different box and I replaced both L&R post-cat) and it took about 30 minutes to replace them both. I saved over $2300 from the dealer estimate.

Glad to have found this post. I'm currently struggling with a "catalyst readiness monitor" not reset also.

Being the cheapo that I am, I tried cleaning the MAF and both O2 sensors (my 3rd gen only has 2, before and after cat). Going to go through the drive cycle and if that doesn't do it, looks like I'll be getting some new sensors.

Thanks for sharing!

Good info.

Sidenote: I've gotten my catalytic converter stolen before when I parked at a rideshare.

I have used Seafoam in my motorcycles for years and I love the stuff. Good to hear how it does wonders in our 4R's.

Oxygen sensors may begin to lose their efficiency after 100k miles. My T4R was well over the 100k mark so that is why I decided to replace the sensors first. Catalytic converters usually go bad from low RPM and infrequent use. I drive mine daily and usually on the highway, minimizing the possibility of cat failure.

What vacuum line did you use to put the Seafoam in?

NExt time, go to autozone and have the codes scanned by them. I had the same one, said bank two sensor two OR catalytic efficiency OR air leak before sensors. I changed out the rear O2 and everything cleared up. You really need to understand that the dealer just wants to do the solution that clears everything without thought and charge you.

BRent

I know this is a few years old, but does anyone know the part #s for the 02 sensors after the cat? I have a P0430 code and would like to try this before replacing the cat.

Can someone also confirm that P04030 is for the passenger side?

Same sensor for rear ! Go to amazon for denso it'll tell you what fits or urdusa has fitment chart but don't buy from them worse than dealer !

That is the MOST common cause. There have been many catalytic converters replaced when in reality it was just an O2 sensor. The ECU throws a code that makes it seem like the cat is bad. But all that means is the the down stream O2 sensors is not sending the ECU a good signal. This can either be a bad cat...OR a bad O2. A good mechanic will then have to run further tests to determine what the actual cause is.

Believe it or not...it's rare for a cat to go bad. They should last the life of the vehicle.

So this seems like a pretty easy do it yourself solution. Can anybody point me in the right direction in terms of how to tackle it? If I know what to do, I'm not afraid to just do it myself.

Rears are easy just need o2 socket ! Now the front is a different story , I think someone just posted fairly recent about doing it . Think they came in below or might even took of tire to get to it .

Where exactly should I be looking to find it? I believe its rear passenger side. P0430 says catalyst efficiency below threshold bank 2. I also looked it up somehwere else that said it was left side catalyst efficiency... Is it left side as in, looking at the motor from the front of the car? Trying to figure out if it's passenger vs. driver. and then from there...where is it actually located?

The rear O2 sensors are very easy to replace. Driver's side front is tough, but doable. I haven't been able to get out the passenger side front as the transmission is in the way. Fronts are for the fuel injection to determine the correct air fuel ratio. The rears are what determines if the CAT is doing it's job based on the info the fronts read

I'm working on a similar problem. I have already replaced my O2 sensors, they can be found on top of the exhaust line approximately inline with front mudflaps. Mine were difficult to get to because the front driveshaft is also right there, but a flexhead ratchet sure helps out. Bank 2 is the driver's side and Bank 1 is the passenger's side.

Here's the thread that I have been using as I try to clear my code.

Good Luck!