P0171 System too Lean (Bank 1) what do replace

[bobdotson]

i have a 97 taco and the check engine light came on and the code says P0171 System too Lean (Bank 1) what does this mean?

thank you all

[canyonquest]

Same problem on my 2002 Taco. The mechanic's best guess was the oxygen sensor. I'll be going to the dealer to be sure since it is still under waranty.

Originally Posted by bobdotson

i have a 97 taco and the check engine light came on and the code says P0171 System too Lean (Bank 1) what does this mean?

thank you all

[Kuch]

P0171 can be caused by an air leak in the intake past the MAF. Look for a hole in your intake boot/hose. Loose vacuum hoses. Confirm all connections, no cracks or leaks.

O2 Sensor is another cause.

Clogged fuel filter too.

[Partyzant]

Have the same problem. P0171. Changeg oxygen sensors, spark plugs & wires, fuel filter. MAF is fine. Still that CE light comes back on. Fuel economy went down by 5MPG or so. Anyone got any ideas???

[cluster1ne2112]

I had the same problem on my 99 when i was towing, dealer said it was an O2 sensor, but when it tested fine blamed it on my lift and 33's... After doing a little research i found that tacomas are prone to having dirty MAFs if they have rechargable air filters. Sure enough i pulled mine and it was caked. I cleaned it up with some evaporating parts cleaner, havent had the light come on since.

[truckpoor]

My 2000 also is doing the same. What is the MAF??? Sorry, can't think of the anagram right now.

Trying to figure it out and have the OEM manuals being sent to me as we speak. Hopefully with that and my scanner I can pick up on something. Tried testing the O2 sensor, but the wiring diagram in my Haynes manual doesn't match up, so hopefully with the OEM manual, it'll have the right info.

A vacuum leak will also cause the light to come on, but I'm hoping against that because I don't want to have to try and find it. Haven't tried the simple stuff like replacing the fuel filter yet. Which I need to do...

[cluster1ne2112]

Mass Air Flow sensor. Its located right after your air filter on the intake tube. Just unplug it, take out the screws, and very carefully clean the thin little wires with some type of evaporating cleaner (like brake kleen) Do not touch the wires with anything. Its kind of a pricey little sensor. then wait for it to dry, and put back in. You might have to reset the engine light once more, but if that was the problem it shouldnt come on again. Like i said, i cleaned mine about 3 months ago, and havent had it come back.

[hobbes80]

Do you guys know the ohm reading I should get when testing the oxygen sensor on a 99 tacoma?

[Pntsplat]

p0171 on the 5vz-fe motor is almost 95 percent of the time directed toward the MAF. usually the platinum hot wire inside gets dirty or oily (K&N filter users) and causes the air volume reading to be inaccurate. The wire heats up using 5 volts and the computer determines the rate at which the wire cools which in return determines the amount of air flowing past the wire. You can try to clean it to save money. Unscrew the two phillips screws and slide the unit out. get some some electrical safe cleaner and gently spray the amber collored bulb and the two platinum wires insde. This will usually take care of it. it not replace the MAF.

[capnray]

Girlfriend has 1999 Astro. Check engine light came on while on interstate. It extinguished before I could scan it. Scan showed P0171. After some research, I went after the MAF sensor, air tube to throttle body and vacuum hoses. I found a downy bird feather in the screen ahead of the elements, directly in the air path of one of the 3 three elements. The single nut on the stud at the throttle body seemed loose also. I did eventually find a vacuum hose in bad, though not split condition. Road test of 1 1/2 hour with an hour stop between halves showed no codes. Consultation with GM tech. confirms that the little feather was most likely the cause of the problem.

[heyyo302]

A code P0171 may mean that one or more of the following has happened:

• <LI itxtvisited="1">The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
• There could be a vacuum leak downstream of the MAF sensor.

Solve it

• <LI itxtvisited="1">In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling <LI itxtvisited="1">Inspect all vacuum and PCV hoses, replace if necessary
• Check for a dirty fuel filter and proper fuel pressure

[dkrgudrgh]