Wow what an awesome response. The rain thing was true for me as well. It sounds like we experienced pretty much the same thing.

I ending up trading my 4Runner in. I had a few other problems with it, and with a kid on the way I wanted something with side impact protection. Thanks for such an awesome response again. I love this community.

My 05 v6 is throwing the code also. I did the WOT test to see if the cat was messed up but it seemed fine. I’ve read a couple threads and haven’t quite gotten a concrete answer on if it’s the upstream sensor or downstream. Is there any way to tell which one is possibly messed up? I would typically just replace one or both and see if it fixes it but my dealer quoted me $312 for a new sensor... 312... doesn’t that seem a bit ridiculous? Thanks

They're caused by the downstream 02s (post cat would be the only way that makes sense).

I just had this for the first time after replacing my leaking cats with aftermarket ones on my v8, so a leaking exhaust was out of the question for me.

It cleared up pretty easily with those blox o2 sensor spacers from amazon, that was the fix for me! $20 well spent!

Sorry to bring up an old thread but I figured I’d update. I took my 4runner to the dealership and they said it needs a new catylitic converter... gonna be about a grand with parts and labor, maybe another 300 if it needs another O2 Sensor. Lovely.. hope this helps anyone who’s throwing the same code

are all the 02 sensors the same pre and post cat?

anyone got any part numbers?

Th upstream A/F sensors should be interchangeable but the downstream O2 sensors are different length harness.

Here's what I put in my V6

DENSO 2344804 Downstream Left
DENSO 2344805 Downstream Right

These were like $100 for both from Rockauto
Denso is the OE supplier and side by side comparison they looked exactly the same as the originals; harness length, connector, hole count, etc.


I was only getting the P0420 code periodically the last couple months, changed both downstreams anyway and left the upstreams alone. So far so good in over 600 km

2 buddies are dealership mechanics and they said dealers and independant shops always push for complete manifold job because it's obviously more money for them but also because they don't' want the customer coming back multiple times for the same problem. What they also don't tell you is they get a nice $100 a pop for the used OEM cats that are supposedly bad.

im gonna start post cat and work my way up.

I don't see/hear any cracks/leaks in the exhaust system so I'm hoping its the 02 sensors.

I'm amazed they have lasted 250k miles.

Great thread gang, I appreciate all the information as I am chasing a reoccuring P0430 code on my 2005 V6, 186k miles truck.

I picked up a code reader so at least I can reset it and not panic when the Christmas tree lights up.

I replaced the gas cap already with a new OEM one., just a precaution. Light went away for a while, then came back last night after a couple of weeks of clear dash. Cleared the light last night when it came back on and it didn't come back on my short drive today.

So I think whatever is causing it is just on the edge of a problem. The right temps, or maybe the wrong puddle, or whatever. No MPG or Power issues so I think it's probably the downstream O2 sensors going OR a small leak somewhere.

I had some exhaust work done about 3 years ago from my excellent local independent. It's possible I've got a pipe or joint farther up stream from the new stuff with a hole or gasket leak of some sort. I'll have them check this first.

Thank you for these!! If my muffler shop doesn't find a leak I'll start by replacing these 2 myself.



I initially searched up this thread to see how long I could go with this light occasionally coming on. Presumably if it's not happening during my State required yearly inspection, and it's not causing power/mpg issues then it's not something I need to panic about, right? I can clear it when it happens and continue to pick away at possible fixes.

There is a nice write up on the previous page about using a shop vac to positively pressurize the exhaust system then look for leaks. You might have a simple leak that's cheap to fix.

Yup, I saw that. I'm going to try it with my leaf blower since my shop-vac is suck-only.

My v6 with 147k miles just yesterday started throwing the P0430 CEL, first mechanic I've taken it to said needs new cat at $750 without even looking at the vehicle. I passed....was going to take to another mechanic to get 2nd opinion. I sure don't want to waste money replacing the cat if that's not the true problem!

"Injection pumps for both banks failure and both catalytic deteriorated. Bank 1 catalytic $1,361. Bank 2 catalytic $1,223 air injector pump assy with valves gaskets manifold vsv #1 vsv #2 air tube and switch valve $2,624.

This was all from a pre trip servicing before I drove from Portland OR to San Diego CA. The VSC/trac//abs caution cluster bomb lit up while I was stationed in Okinawa and my mom was driving my 4Runner. The service team is saying this wouldn't be normally this bad but it was ignored and condition only got worse. I don't want to sound all conspiracy theorist, but I just think they're trying to get me when this could be just as simple as a gasket or a sensor. They "strongly advise repairs or new car instead of driving into total failure of air pump"

I work in Naval Aviation and we don't just change engines or transmissions or rotor heads based on a general discrepancy. We troubleshoot and then make repairs before remove/replace.

I'll update once I get the actual code the ECU popped the CEL.

Got the printout and it says my 4runner is throwing P1442, P1445, p0420, 4030, 4040

I've had my 2004 V6 4Runner for about a year now, so far it has popped up with a P0430 code 3 or 4 times. I would like to do more diagnostics to find out why this is happening, but since the code comes up so infrequently it seems like it isn't worth the trouble. Right now I just clear it with a scanner.

Has anyone else had theirs go months in between tripping a trouble code?

Mine was going 2-3 weeks in between.
Here’s what I learned , the computer does a check on the downstream O2s once per key cycle, and only after the cats are nice and hot. So if your driving sessions are short you might not get to the point where the check is done.

You can examine for exhaust leaks first and test cat temps , those are easy and but generally if your going some time in between P0430/P0420 codes it’s most likely the downstream O2.