malgyver

Hey there,

I recently went to get my 99 Pre-runner V6 smogged, and told the mechanic that the Check Engine light had been on for some 30K. I am a mechanic, and didn't noticce anything drastic, and too poor to deal with the problem.

They read the code - P0171 which says the fuel trim is set too rich. The mechanic told me the truck has a lean condition.

After spraying some (brake?Carb?) fluid around the upper/lower intake manifold joint, the O2 sensor readings fluctuated, as did the idle slightly. The mechanic is convinced that the Intake gasket is leaking enough to cause this code.

He had it hooked up to the smog machine, which read about +19% for Sensor 1 at idle, and +99.2% for sensor 2, with the voltage output of the sensors seeming, I think fluctuating between .03V and .8V.

Does the P0171 code indicate the computer trying to richen up to compensate for a lean condition, as the mechanic said? Do you think that the reasonably small intake leak will cause this problem? The mechanic said the first thing he would do is reseal the upper/lower intake gasket.

Finally, is there any way I can reset the light myself so when I do each piece of work, I can determine whether the repair fixed the problem?

I already planned to clean the MAF out, as I have read on earlier posts in the archive, but wanted to know more about the possiblity that this minor vacuum leak could also be the culprit.

Thanks!

toyotaoffroad91

yes..leaking intake= sucking more air=more fuel=richness (not in your wallet) but that should be a simple fix

mattbabino

Take the Neg.terminal off the battery for 5 minutes. This should reset the computer and clear the Engine Light

toyotaoffroad91

you can also pull the efi fuse this will reset the light and the ecu

rimpainter.com

I don't advise pulling the NEG or a fuse. Fix the problem first. This particular code is probably related to a dirty MAFS. Search this forum by the code and you'll see thread after thread regarding this code and what to do. Good luck.

MTL_4runner

While the P0171 "lean condition" code is most often associated with a dirty or bad MAF sensor, it is possible that you have an unmetered vacuum leak that might also be throwing the same code. I would be interested to know exactly where he was spraying the carb cleaner and where the mechanic thought the leak was. It isn't very often they an intake gasket just gives out unless you have removed for some reason in the past (such as adding or removing a supercharger). I agree with Christian, fix the problem, don't just reset the code.