what up everyone , i have a 2005 4runner sr5 and today the vsc, vsc off the traction control light, and the check engine lights (which I got code 420 which is a o2sensor) came on. I rest the code and all the lights went out, about 20 miles later there all back on Any help would be great

Gas cap, I had the same problem.

Yep, don't argue, don't over think it and quit looking!! Gas cap is loose or bad!! Replace or tighten!! If you disconnect your battery for 5 minutes after replacing / tightening the lights will go out and stay out!!

WELL, I just got done eating a 3 1/2 pound crow. Jason, all my lights were on just like yours. I did a search and found the gas cap answer. I put on a new gas cap, unhooked the battery for 5 minutes, hooked battery back up and all was good FOR ABOUT A WEEK!! That's why I answered the way I did. TODAY THE SAME LIGHTS CAME BACK ON!!! Grrrrrrrr!!!! I hate to take my runner to the dealer to have them start replacing expensive items until the find the right answer accidentally. Mean while the lights will be out a week at a time until they luck out!!

A P0420 code is not for an 02 sensor, its your bank 1 catalytic converter not working properly. you will only be able to get your CEL to stay off for small periods of time before coming back on. the only way to keep from having a P0420 come back on is to replace your bank 1cat

Paul, I am going to guess that the cat is expensive. With 36K on my runner I would expect it to last longer. Either poor cat or poor gas!!

cats are expensive unfortunately. most usually have a longer life than what yours have unless their is an issue with gas or if the spark plugs are fouled

UPdate on this thread. Just took the runner into Toyota. They ran diagnostics and said the cat. converter was bad. Said something about it and a manifold and $2000. Then he tells me all covered under warranty. All parts ordered and appointment for next week. COOL!! FREE is COOL!!

Yep, I had this happen a few times; once it was the cat like you're saying, and the other times it was the O2's.

Ding Ding we have a winner!!!!!!!!This is what they just replaced under warranty. They also said something about the manifold being cracked. At any rate so far so good and FREE, FREE is good!!

I have the 2003 4 liter 6, sport edition 4x4. Engine light came on, code reading indicated Catalytic converter malfunction, bank 2. Also VSC Off and VSC Trac lights came on - all the time.

I was ready to replace lots of stuff for lots of money.

The big help was " Stop over thinking this - buy a new gas cap". For $25 the problem appears to be fixed. I did remove the negative cable from the battery and let the systems discharge for an hour or so.

It appears that somewhere in the computer decision tree, it thinks that if the emission system isn't working right, it would be a good idea to disable the traction control system. Doesn't make sense to me, but I'm glad the gas cap fixed it.

Thanks for the help in the thread.

2003 4x4 limited here with same issue. Mine are he bank 2 cats that are bad (apparently). Anybody know if the bank 2 cats are the hard to get to ones? If they can be replaced with aftermarket parts and welding, I can save a lot of bank.

Of course, I'll try the gas cap trick first.....

You guys need to let your 4runners idle and warm up for at least 30 seconds (best is a minute or better would be two) before you start driving, especially with the V8's - then no more broken cats or exhaust manifolds. As for the gas cap... minimum 3 clicks!

Learn to be patient with your 4runners... step one - wait for the backflip, and just be patient as it takes time.

I have had those stupid lights on for over a year. Just read this post, went out and tighten my gas cap 3 clicks and they are now off ! Thank you.