Hey everyone. I just got the 4runner ('99 with 130K) and I was doing some minor service work (fluids, greases, airfilter) and after I changed the PCV valve, I started getting a code 420, which I read is the catalytic convertor or the O2 sensor... so is it just a coincedence that right after i replaced the PCV valve the check engine light comes on? if anyone has any ideas just let me know. Also, if it is the O2 sensor, which one? i have 2 cats (cali maybe?) so let me know. Im all new to this.

Patrick

 

Interesting. We have a '99 with a 420. Keep us posted...

 

Just do a search for P0420 .....there are quite a few thread on this to read.
If you still have questions on what you tried, post back and we can help.

If you do replace an O2 sensor to fix it, typically the one closest to the engine is the one that fails first.
This code is usually either an O2 sensor or a cat (yes, cali versions have 2 cats)
Also on 99-02 4runners, the front sensor is an A/F sensor not an O2.

https://www.yotatech.com/search.php?searchid=1100491

 

I just had the same code 420 in my 99 with 70K. I had the code show up 3 times with no other codes. On the third code I took it to the Toyota dealer in Alexandria VA. Because mine is within the 8 year 80,000 mile warranty they fixed the catalytic converter for free. Mine has the California dual cat system...don't ask me how...the 4runner was purched new in VA and has always been here. Also, the new cat has a sticker that says it's for a landcrusier but it appears to be identical to the one that came off. If it is an O2 or A/F sensor it should have a code stored in the ECU for that and tell you which sensor is not sending a good value. Patrick you have a A/F sensor up front if it has dual cats and that sensor is like $220, you probably want to have it tested before just trying to replace. I think the only way to tell if it is the cat is to take it and have it emissions tested, thats what they did with mine. Good luck

 

420 --->