nanomatrix

OK, I have this intermittent engine light problem which I have been trying to solve for the past 8 months. Two of the Bay Area dealers originally passed it off as the gas cap wasn't fitting properly. An independent engine scan brought up the P0171 code.

My latest effort was to clean the MAF sensor...which was good for about 60 miles. Now the light is back on. Now one thing I noticed was the the o-ring had a couple of sharp crimps in it. But I oiled the ring and replaced it ,then reset the ECU from the fuse box and everything seem alright. Actually I picked up a nice boost in my mileage after the ECU manged to reprogram itself.

Anyway I'm not sure what tackle next. Could the o-ring be a problem? should I go after the O2 sensor, or just pour some fuel cleaner in the tank?

Thanks
nanomatrix

rfakinbile

I'll suggest you allow the CEL to come back again and have the code read before going ahead to do anything. What are the symptoms of problems you're experiencing?

nanomatrix

No symptoms other than a slight drop in mpg and CEL.
But my plan my plan for tomorrow is to get that code.

rx300s415

Sorry to hijack the thread, but how do you reset the ECU through the fuse box?

Lexmex

https://www.clublexus.com/forums/sho...8&postcount=15

Lexmex

O-ring can be the problem, as even a tiny hole or issue can throw a P0171. You also have to check all the hoses related to the air intake system, including those going off the airbox. Some people have gotten the P0171 and it has been an issue related to the top of the airbox not being secure over the bottom piece and a small fold developing. Other possibilities do include the fuel injectors having blockage, exhaust pipes (namely immediatley off of the manifolds developing a leak) or the engine coolant sensor.

smerre01

Well the P0171 code relates to air-fuel ratios. Usually the car is running too lean in most cases. i.e. if the car ran out of gas and had no fuel but was able to get air it would throw the P0171 as the car was too lean. There are a host of things that could create this problem. First thing to check to me would be the air filter, make sure it is clean or lightly used, if it is heavily full of debris the car can run rich causing the P0171 code. From there I would say replace the Heated O2 sensor. The signal from this particular sensor indicates whether the air-fuel ratio is too rich or too lean. It basically triggers a reduction in fuel if the car is running to rich (too much fuel), or an increase in fuel if the car is running too lean (not enough fuel).

After that it could be the fuel pump/filter, a clogged or dirty fuel injector, the mass air flow meter, or the engine coolant temp. sensor. I would take it systematically though. Putting some GOOD EFI cleaner in the car wouldn't hurt it to do first though. Toyota dealer sell a toyota brand that is apparently pretty potent as you have to run the gas out of the tank pretty quickly in order to prevent damage, lol....I guess it is like drano for injectors. However let us know what you determine I am sure that there could be a host of things causing this, and it is a good thing to know how it was resolved.

nanomatrix

OK, Round Two.
The new error code is P0440.- General EVAP Control System Malfunction - nothing specific. Probable air leak somewhere in the fuel system.

One other data point; when I remove the gas cap there is no hissing sound. hmmm. Gotta be one of the hoses. So I check the Air Filter box closely.

What?? The CCV hose isn't connected to the Air Filter housing.
I find the hose everything seems to be intact so I attach it and reset the ECU.

I put about 20 miles on it this evening, no CEL. Let's see how long this lasts.

PS. Thanks for all who tried to help. No, I haven't tried to see if the gas cap will hiss. I'll do it tomorrow.

nanomatrix

Just a quick followup.
After a couple of hundred miles, no CEL and I'm getting better mileage.

I took it to one of our CA Smog Testing Stations yesterday.
After 15 min on the dyno it passed with flying colors.

Thanks