I had the same engine light problem on my 2000 4runner. After $300 worth of diagnostics it was either the mass airflow sensor or O2 sensors (there are two, upstream and downstream). I replaced the MAFS (very easy) and pulled the computers fuse to reset the code, providing about a week of relief from the light. Next I ordered the upstream O2 sensor (have the dealer check to see if you have CA emissions to order the correct part) and replaced it (also very easy) and voila, the light disappeared after a bit of driving. As short as my story is, in reality, it was a long drawn out process that was my fault for trying to save some $$. Anyway, I hope this helps.
I will cut the check light cable when I get my 4runner... the computer indicates too many checks. i think it can be a simple error of the sensors... that is annoying!
Your question regarding the P0446 EVAP vent control malfunction, have you checked the vapor lines that run to and from the tank? If the gas tank is not properly pressurized it will set this code. Also make sure your pump seals are good and you have no cracks or pin-holes in the lines.
Something to consider: if your cat converters are going bad you'll smell sulfer. Remember - no smell no cats.
I live in Mass. If you have an engine light on for whatever reason, you will not be able to get a sticker, which is a yearly hassle to begin with. I have a 4Runner and Camry and both of them have engine lights on and both cars run perfectly. From what I hear, this is a big problem with Toyota's. Besides that, I wouldn't buy another car out there because they have proven to me over the years to be the best out there.
I am sorry to say, but I'm a mechanic and you have been HAD! If the check engine light illuminates once and goes off, you have a few miles to go before it gets deleted. I can't tell you if it's 1,000 or 10,000, but most of the time these check engine codes don't just disappear. If the dealership hooked up the code scanner, all of these codes would have showed up on the computer screen. (even if the check engine light is not illuminating at the time of diagnostic.) It would even tell you how long ago it happened and if it's a reoccurring problem.
The dealership knew there was a problem with your CAT converter. They also knew it would be very expensive and they would have to repair it at a loss. They weren't going to fix it for you unless they absolutely had to. Most of the time the mechanics are not allowed to share what they find with the customers. They are told to keep a tight lip about certain stuff. You should have gotten a second opinion at another dealership. I'm sorry to say, but you had been ripped off by Toyota. It's the same old story when they had that V6 Toyota sludge problem and they tried to pass the buck to the consumer instead of standing behind their product.
I think Lexus doesn't have this problem. But bear in mind that every dealership is different.
If your 4runner is a Calif. emissions spec vehicle, it will be equipped with 2 catalytic converters both monitored by one oxygen sensor. Thus their indecision about whether just one or both may be deficient. The sensor is located behind the rear catalytic converter, & so logic would say that this is the one that would most likely cause the p0420 code, since if it was working correctly, it would scrub the exhaust gasses efficiently enough to keep the light out, assuming the front one was working also.
However, because the same sensor monitors both, the front one may have failed as well. They were actually doing you a favor when they suggested to replace them one at a time to avoid doubling an already costly repair.
Also it should be noted that Calif. emissions spec vehicles are sold throughout all 50 states, not just in Calif. So in any of the 49 states you could have either a Federal (49 state) or a Calif. spec car.
I'm a 25+ year veteran of repairing Toyotas & other Asian vehicles. I'm ASE certified Master Technician & also Toyota factory trained. Fuel injection/ emissions & electrical diagnosis is my forte'. I hope this was of some help.
2003 Toyota 4Runner Sport Ed - At 100,400 miles, my car starts sputtering and eventually won't start. Toyota says need to replace both catalytic converters at about 2K. Live in Cali and never had to smog new car until now, and won't you know, I can't get smogged due to my issue. So not fair! How can 2 converters go bad? I don't drive crazy, and I change oil every 3-5K miles by the Toyota dealership.
Anyone out there with a similar problem and like vehicle?
Should Toyota add this to their LIST of recalled vehicles?
After 150,000 miles on my 2000 4-runner, the check engine light threw the p0420 code.
Same with you guys, Toyota service quoted the dual CAT replacement at $2000.
I only want to pass emissions to get re-registration.
Toyota warned that the cheaper aftermarket CATs might work for awhile but then go bad - but heck for 1/3 the cost, I was willing to take the chance.
I bought a front California emissions CAT for $300 and had that installed. (Just did the front one first)
The po420 cleared, and I passed inspection.
Two months later the 420 came back, but I have my registration now which lasts 2 years. I will replace the rear CAT the next time around.