Sorry for the long post but here it is:

Ok so last night, in my 2000 4runner with 98.5K on it and has had all maintenance completed in the book by a local toyota dealer with a good rep, I took an off ramp that merged onto another highway and about 3/4 the way through the turn my CEL comes on. I slow, then give it some gas and there is still power like normal. I get off at the very next exit and drive about 1/2 a mile up and pull into a well lit parking lot. I check my oil and there is plenty of oil and it still looks nice and clean( I had my oil changed by a place that didnt thighten the filter down all the way and leaked out about 1.5qts in 2k miles so that was the first place I started), I start listening to the motor and there is no noises out of the ordanary. I shut the car off and disconnect the battery. Let it sit for about 5 minutes while I continue to look over and reconnect the battery and start the car and no CEL. I get back on the road waiting for the CEL to come back on thinking its only a matter of time. But it never came back on. Not even after sitting in traffic for about 35 minutes. Its still off now, but I am trying to think what would have caused it only to come on temporarly? Could it be an O2 sensor? I have been getting around 16-18mpg driving mostly highway with some city tossed in there. It was odd becuase the light just came on and there was no shutter or anything. Any help would be great. i thank you all in advance.

 

Okay, so next time, have the code read so we won't be guessing...

With that said, it might take a while for the code to reoccur, if it does so at all. Most of the monitors require a VERY specific "drive cycle" or sequence of events before they reset. That can include some very specific requirements, like starting from cold and warming up to a certain point, various driving speed combinations, etc. Depending upon your driving habits, that can take days or weeks. Some monitors even require those conditions to happen twice before they will throw a MIL.

There's NO way to guess at what the code was. If you want to know, don't disconnect the battery next time.

 

If you *really* want to understand what is required to reset the various monitors, have a look at this from my site:

http://www.watrd.com/work/TSB_EG003-02_(revised).pdf

 

Disconnecting the battery will erase the ECM memory, and clear the fault code(s) preventing further diagnosis. With the fault code erased, the MIL will go out.

What you should've done is drive the vehicle to any shop with an OBDII scan tool, and read the code.

What you do now is continue to drive the vehicle normally, and when the light goes on, go to any shop and find out what the fault code is.

P0171 (system too lean) is very popular, and caused by a faulty/dirty Mass Air Flow Meter. Longest lasting repair is to put a new one in. Most dealerships have these things in stock.

HTH.

 

i've been plagued by a cel for the past year or so.

p0420 every time, zero drivability issues. apparently the toyota ecu is VERY picky about what it likes to see the cat(s) doing.

funny part is that the cel turned off about a month ago, on its own, and hasnt been back. wierd.

next time have the code pulled, autozone usually does it for free, at least that way you will have a starting point from which to do your search.

 

Well good new (i guess) the CEL just came back on this morning. I am going to roll over to autozone and get them to pull the code for me so I know what I am working with. Good thing I just had my emissions done a few days prior to the CEL first coming on or I would have failed and lapsed on my registration. WHEW close one!

 

My congrats goes out to 86tuning with the p0171 code suggestion. You hit the nail right on the head. I am going to pick up a new MAF on monday morning. Thanks for all the help!

 

Why not just clean it? 99.99% of the time, that solves the problem.

 

If I cleaned it how long would it the fix last? What would be the best thing to use to clean it? Brake parts cleaner? Or Carb cleaner or are those to harsh?

 

If you buy a new one, how long before it gets dirty? If I clean my kitchen, how long before it gets dirty?

It depends upon how it got dirty in the first place. If you are running some nasty oiled filter, then it will start immediately.

The cleaning process is pretty simple. Do a search on here for threads related to it and you will find many that describe the process in detail. Both brake and carb cleaner will destroy the maf.