jim1000

My "check engine" came on the other day, so I pulled the OBD II code and it told me "running lean (bank 1)" -- code P0171. What does this mean for my 1999 4Runner SR5V6 with 80,000 miles?

Thanks.

potroast

do you have the S/C? running lean means you arn't getting enough fuel mixed for the amount of air comming in.

jim1000

I don't have an S/C. Also, I did NOT run out of gas.

Dr. Zhivago

It most likely means your MAF sensor is dirty. This topic has been beaten to death. Please use the search button.

Peace.
G

Wheels_tech

The code means you're getting too much air or not enough fuel. Could theoretically be caused by a faulty sensor as well.

Have you changed anything on your truck lately? If not, you'll definitely want to check your O2 sensors which I believe to be the most likely culprit. You might also have a vacuum or other leak somewhere.

If you've recently changed your intake or something along the intake path, then likely there is a problem there.

Other possible problems could be fuel filter (but might possibly show different codes), injectors, fuel pump. Basically you're looking for something that will cause less fuel or more air (a "lean" condition).

Hope that helps a little.

-W

jim1000

I've tried using the search feature. It was not helpful. By the way, do you mean MAP sensor? What is a MAF sensor?

jim1000

[QUOTE=Wheels_tech]The code means you're getting too much air or not enough fuel. Could theoretically be caused by a faulty sensor as well.

Have you changed anything on your truck lately? If not, you'll definitely want to check your O2 sensors which I believe to be the most likely culprit. You might also have a vacuum or other leak somewhere.

My car is bone stock.

potroast

No, he definitely means the MAF... Mass AirFlow... It's in the intake tube near the cleaner box. It measures air coming into the intake, and that's what's used to determine how much fuel to add.

Unhappy99

There is no MAP (Manifold Absolute Pressure) sensor on your vehicle. There is a MAF (Mass Air Flow), and its dirty. They get dirty every 30K miles or so.

Clean the MAF

Pay attention to MAF4.jpg and MAF5.jpg, being sure to clean the hotwires themselves. Spray carb cleaner works well, and its a 10 minute job.

Wheels_tech

I stand corrected. Looks like the most likely culprit is the MAF sensor. However, with the earlier Gen3's cleaning it is not such a straight-forward proposition. I was planning to do this when I did the deckplate mod, but after I looked at the extremely poorly designed MAF sensor, I didn't bother. I was trying to figure out what the heck Toyota was thinking when they designed or chose this thing. I thought the one on my Lightning was bad since it has a solid post that blocks about 10% of the area of the pipe, but this one must block at least 25-30%.

Luckily you have one of the newer gen 3's.

dragr1

iTrader: (3)

I got the same code and ignored it for a while, but eventually it got bad enough where at full throttle I had zero power. I cleaned the maf and no change, so I replaced the maf and it fixed the problem.