2000t4r

My CEL has been on for atleast the last 40K and it was code P0171. I never replaced the MAF only because I did not want to spend the money. Plus the truck was driving fine and still getting ok gas mileage. Well today while I was driving to work my CEL turned off. I thought that the light bulb burnt out, but when the ignition is ON the CEL comes on.

Any ideas on why the light turned off? DO you think the problem some how solved itself?(I realize that things do not fix themselfs)

humanoid

Although the CEL may be gone, the computer may have still stored the code in memory. If memory serves me correctly, P0171 means your fuel system/engine is running lean. Check to see if your MAF is dirty or not. If it is, you should clean it.

http://www.4x4wire.com/toyota/mainte...tenancep5.html

and scroll down half a page...

blzorro

Attention all: The cel was on in my runner and i put lucas fuel treatment in and it went off ever since.

midiwall

Humanoid has it... P0171 is System Lean, and the most common cause is a dirty MAF (followed by the front O2 sensor).

There's a OBD II reference chart here:
https://www.yotatech.com/forums/f128/obdii-trouble-codes-76363/

It may have gone off 'cause something happened to clean the MAF (kinda' weird, but okay), or there was some carbon deposits on the O2 sensor and they finally dislodged (better possibility).

It's really important to pay attention to the CEL lamp. Remember, it's an "idiot light" and they have a tendency to come on when there's impending doom - not "oh, when you have a chance, can you get to this?".


Attention BLZorro... Without more data, that's bad advice to pass around.

2000t4r

Yes I understand that when the CEL comes on it needs to be handled right away. When I scanned the code teh reader stated that the truck was safe to drive, this was also confirmed my a service tech at Toyota. If it were something that would cause the truck to explode or cause it to not be driveable then that problem would be fixed asap, no questions.

midiwall

Okay, so you're in the newbie section hence the light tap on the wrist versus a full fledged assault.

Maybe I shouldn't have paid attention to that...

40,000 miles running LEAN will RUIN your engine. It will cause pinging, high heat conditions, premature wear of most everything critical. You also have to keep in mind that once the CEL is on, you will never know if another code doesn't pop in behind it. It could be related, it may not be related. The point is, you won't know.

Engine misfires, toasted O2 sensors, blown exhaust gaskets from too much heat, blown HEAD gaskets from too much heat, burned pistons (from too much heat), burnt valves (from too much ______).

Running for 40,000 miles on a CEL is not a good idea.

Running for 40,000 miles on a LEAN condition is flat out dumb.


And my guess is that if you asked the makers of the scan tool, or that Toyota "tech" what the definition of "safe to drive" is, it wouldn't include the phrase "Yeah, 40,000 miles sounds about right".

2000t4r

Well thank you for the lesson. I'm well aware of what a lean condition can do to an engine; this is not my first car. If the truck was running a lean condition then I'm sure when we checked the pulse of the injectors we would have found something wrong them. Random checks of the data port is what was done to ensure that there were no other CEL codes that needed to be addressed.

I don't need to have you address every response as if you are the only one is the world that knows about these trucks. If I wanted to be lectured I would call my Dad (who was a mechanic for 25 years) or our friend of the family that owns his own repair shop (and has been a mechanic for 30+ years).

Thank you for your help since this is something that I had never seen before on any car. CELs don't just turn off; there is no miracle liquid that can fix a CEL.

midiwall

Okay... So if you had mentioned the injector checks, and the random OBD readings then that may have helped up front. But fwiw, validating injector pulses doesn't mean that the injector is actually opening, or that there's adequate pressure in the fuel rail.

SOMETHING tossed the CEL.


btw... Posting in the newbie section will get you treated as a newbie. Not everyone watches this section, I try to and I happened to pick up the thread. I'm online a lot and I try to help when I can.

But since you have 55 years of experience standing behind you, and you claim to be no newbie, then why not toss this out in the real world where it may get more exposure.


fwiw #2 - I DID give you straight info on what may have happened to clear the lamp. You took off on my criticizing you for driving with a CEL for 40k.


Actually, they can. The ECU constantly resamples the condition. It will take a number of ignition cycles and driving time to do it (varies based on the condition) but the ECU can flag the condition as cleared.

oop... sorry, I'm passing along information again. If only I had the experience in stuff like this to back it up. dern.

2000t4r

Well again thank you for your help and I did not post this in the newbie section someone moved my post. I started this in the tacoma/4runner section.

BTW the light came back on today while driving around my job site so I will check the code today and figure out if it is still the same code and let you know.

Thanks again for you help.