My response is quite repetitive, but since this Forum has once again proved its importance I wanted to provide my scenario. Recently took my car in for its 5k mileage check - all came back fine. A day later I was driving and had VSC, Trac and Check Engine lights pop on. Quite annoyed since taking my '02 4Runner with 175K miles to the dealer these days never returns good news.

I went to the forum and obviously noticed a trend. AutoZone read the codes, resulting in the following:

P0446 - Evaporative emission control system vent control
P0420 - Catalyst system efficiency below threshold - Bank 1

Similar to other posts, I unplugged the positive side of the car battery and purchased a new Gas cap. Lights went out!! However, when idling the car is shaking quite a bit and "skidding" for a split second when I come to a complete stop. For now the lights are off, but I have a good feeling tomorrow (or some point this week) it will return. Until then, Im good...if the situation changes I'll be sure to update anyone with outcomes/solutions.

Thanks again for the assistance!

Had the same lights pop up on me last week. I went ver this thread and changed all 4 o2 sensors and reset the computer by pulling off the positive battery cable. Light went away and I got a full tank of gas. Ran fine till I got down to about 1/4 of a tank lights returned. I was at 1/4 of a tank the first time I got the lights. I will be changing my gas cap and resetting the computer tomorrow. I will be back with results.

So I just changed the gas cap and reset the computer again. Drove about 15 miles no codes. Decided to fill up after the drive. So when I get back down to 1/4 tank again we will see if it comes back.

So cel and same codes returned about 20 min after my last update , changed all the vacuum lines and exhaust gaskets. The gaskets on the driver side cat were down to just bare metal. Driven a couple days now and no lights hope this it.

Glad I found this thread. I had CEL, VSC light on and flashing. Was about to go to dealer, then read here to tighten gas cap, and remove positive battery lead and reconnect (to reset sensors?). When I started it up, lights are off. Hopefully will stay that way. Thanks guys

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2008 4R Urban Runner.

Wow, well at least I am not alone with my 4Runner dash suddenly looking like a Christmas tree.

So this morning when I was leaving for the airport (why does this stuff always happen when you really can't deal with it?), I got the check engine and VSC lights. I'm hoping it is something simple. When I get back I will try the gas cap. I did fill I up a couple days before this happened. We also just had a pretty big storm that I was driving in, but that was a couple days back. Lots of possible causes of different problems, it seems.

I do have a question though as I only see one other post in this thread mention it: how many people with this issue had a noteable decrease in performance? My 4Runner idled fine other than being low (about 500-700), but was very low on power. The odd part is that if the pedal was floored, it would only do about 45mph, but I could ease it up to 70 mph if I was barely on the gas. It would do fine until I was on any kind of an incline and then it was steadily loosing speed. Seemed like it was in some kind of "safe mode"?

Fwiw: I have an '05 SR5 with the V8. The thing is also from the east coast so it does have rust and the ever present exhaust tick from hell. I'm hoping that this issue isn't a sensor because I hate throwing expensive parts at a problem without knowing 100% it will be fixed.

Does anyone know if the sensors use the exhaust system itself as the ground? I'm thinking that might be the issue if there is a major exhaust problem. Oddly enough, the engine sounded quieter, with a lot less ticking.

If your check engine , vsc trac, and vsc off lights come on. And if the gas cap retightening didn't work for you, as it didn't for me, here is the solution if codes indicating "Bank 1 or 2 Lean errors". First some history, I had the dealership replace both the O2 and A/F sensors on bank 1(passenger side) 3 on separate visits. I have an 03 4 Runner. I also personally replaced the O2 sensor twice and the A/F sensor once at $100 to $200 a pop over an 18 month period!! Toyota had a service bulletin come out on this problem in 2007 or 08 but I had to bring it to their attention!?! I finally permanently solved the problem myself because three separate Toyota mechanics were clueless. Buy and install a product from the 50's and1960's called a "NO FOULER" between the tailpipe and the sensor. The cost for this part was $0.69. That's right sixty nine cents. I found them at Pep Boys(not everyone sells them anymore). The product was originally designed to stop spark plugs from getting fouled with oil which was common problem back in the day. I've been trouble free for 4 years now. This is very easy job for a diy kind of guy or go to your local garage. If they charge you more the 30 mins labor they are ripping you off. Make sure to take the "No Fouler" with you because I can guarantee you that 99% of the garages have never heard of this solution and I'm not sure if the dealership will agree to do it. It must be fixed asap because your mpg will drop from 20 something mpg to 12 mpg as mine did. The reason for that is because the sensor is sending a msg to the CPU that the fuel is too lean and mistakenly 'richens it up too much'. First try using the old sensor with the "NO FOULER" before buying a new one. P.S. If you do buy one, make sure that you buy a Denso sensor or you'll regret it. They are the OEM for Toyota. They can be found on ebay for 50% of the dealer cost, which is about $200. Good Luck

2006 SR5 V-6 with 67,000 miles. Replaced the gas cap, disconnected the battery and all appears well. Great info on this Forum-

THANKS!

Pete

Thank you everyone for the info. My CEL came on on my 2015 Limited. After checking this thread I tighten my gas cap and disconnected the negative battery cable and all is well. Thanks much appreciated.

Sorry to hijack this thread but I'm new and not allowed to post yet. I just bought my son a 99 4Runner limited with 166k miles. The previous owner had it smogged 3 months ago and I had it smogged day after I bought it. Both times passed with identical results. 4 days later the check engine light came on. I had the codes read and came back with something in the cat. Took it to my mechanic who did a diagnostic and said it needed a new car and o2 sensor to the tune of $800+. Since I just had it smogged and it's being driven by a 16 year old driver I decided to wait on the repair for now and watch for overheating etc. Well a couple days ago the light went off and hasn't come back on. What could cause this? Should I still have the cat replaced? Anyone else experience this?

Last week my VSC, TRAC and Check Engine lights went off...followed the directions from this post (which was started 10 YEARS AGO!) Replaced the gas cap, disconnected the battery and all appears well. All Good!!!

Same here. You can get the OEM gas cap for $17 or just an OE gas cap for $8 on Amazon.

Add me to the list. will post when gas cap and battery fix are completed.

Battery cable disconnected and reconnected gas cap tightened = problem solved.

Warning lights returned so I paid for a new gas cap (seal on the old was nonexistent) cleaned the battery cables and studs and sprayed them. Reconnected. Lights are off. Will see if they stay that way.