I looked on Gadget's URD site for O2 sensors and it looks like they indeed made all 4runners 50 state legal in 2001. So that seriously stinks because it means you really don't have any choices except to pay the dealership for the precat at the very least (which I am sure is huge $$$$ just by itself).

On both Tacos and 4runners it looks like 2001 was the changeover year:
http://www.urdusa.com/product_info.p...s_id=430006000

 

Matt - have you gotten the code lately? I changed my plugs and cleaned the MAF. Got a code immediately but cleared it and haven't since - a couple thousand miles.

 

Yes, it still comes back every few weeks or so.

Matt

 

Matt, you should at the very least change out the front A/F and rear O2 sensors unless you want to pay for daignostic time to verify if they work or not (sometimes even then they won't "look" bad, but performance has dropped enough to cause an issue with the ECU). That way you start with a solid base on which to do diagnosis with the cats if they indeed are the issue in the end. I know no one wants to replace parts that are good, but sometimes that is the fastest way to rule things out without spending huge numbers of hours doing diagnosis. Start with the rear cheaper O2 sensor first, reset the ECU.....if CEL returns, read the code, change the front sensor if the code is the same.....if CEL returns, read the code, change the converters using OEM parts (yes, expensive I know but I haven't seen the CA spec vehicles do well with anything but).

 

I jinxed myself or something... Yesterday we took it out and did some slow crawling for a few hours - some long, steep ascents and descents - and it came on *twice*.

 

I mentioned earlier in this thread that I am experiencing the same thing Matt & others are experiencing. I changed out both sensors and the code went away...for about 18 months. Now I am back to where I started. I am having trouble finding someone to do the oxygen capture test that Gadget recommends. I am guessing the cats will need to be changed out.

 

Is your truck high mileage as well?

 

Couldn't it be that your cats are going bad? It's a major thing for us Cali folks as we need to pass smog every two years. I'm going your route and swapping out both sensors and see what happens. 18 months w/o the CEL is not great but better than it popping up every time it's cleared.

 

115,000 miles on the clock.

 

Are both sensors the same?

 

That's not really excessive mileage so i'd be surprised to see the converter go that early unless the cat was somehow damaged from overworking (such as a prolonged rich condition).

 

I'm in the same boat with the P0420 code. Right now I'm torn about what step to take next.

Option #1
Buy a cheap OBDII reader ($50 range, as I don't have one at all), replace the after CAT 02 sensor and see if that helps. If that doesn't help replace the Air/Fuel sensor before the CAT and see if that helps. If neither work, then I'd take it in to get OEM CATS

Option #2 (and really my question)
Buy a nice OBDII reader (http://www.canobd2.com/tool/3130.asp <---can get for $160 shipped or http://www.auterraweb.com/dyforwiusb.html <----about $190 shipped), both of which offer "Oxygen sensor monitoring and on-board test results" in hopes of determining if the 02 sensor/Air-Fuel sensor is the problem, instead of just replacing them (they cost about $300 combined). If they are bad, I would obviously replace them. If they show good, then I would have spent the money on a nicer OBD reader, but saved money I didn't need to spend on the sensors. I would then head straight to attacking the CAT problem.

Suggestions on choosing option 1, 2 or other?

Can those OBDII readers reliably report a bad 02 sensor (and do they scan the A/F sensor, or is it different than the 02 sensor)?

Wanting to attack this problem in the smartest way....and if I can get a tool that I'll get to keep for a long time and prevent replacing parts unecessarily, I'd love to do that.

Apprciate the help!!

 

Just thought I'd add my two cents worth here.....

As a smog tech here in CA (last 30 years) we use a Raytek Raynger ST2L infared temp gun to check cat shell temps...I non working/weak cat will be much cooler than one that's is good...and like many here have stated CA uses 3-way cats (HC, CO & NOX, First bed in cat stores oxygen) As our trucks get older the Bank 1 O2 first sensor can get lazy...lazy meaning that it does not switch from lean to rich as fast as it use to....funny thing is that there is a code for this too but it can degrade quite a bit before it will actual set a code...this effects emissions and mpg when it gets lazy too. The back O2 usually does not go bad as quickly as the front O2...less heat in the rear, kind of rare to go bad too. The O2 sensor in the rear in a good working system will stay fixed in voltage or there abouts...when it starts to swing (high to low voltage) only then will it tell they pcm that one or both cats are failing...it does not know which cat or a combo of both are...and yes these sensors are different and can't be swapped.

 

The cat goes bad when excessive fuel enters the cat and burns in the cat ,or if oil is entering the system ang cloggs the system. Check the codes,and the 02 sensor.Stay away from the bosch if one is needed.GO stock or denso.