Check engine light code P0171 activated on my 2001 toyota corolla

A P0171 means that your Toyota is having trouble with a dirty or faulty mass air flow (MAF) sensor, or a vacuum leak downstream of the MAF sensor but this code can also signify a bad O2 sensor in the exhaust on bank 1.(the one closest to the engine on bank 1)
Also, P0171 code can be tripped by a plugged fuel injector, by a dirty fuel filter causing low fuel pressure, or even an exhaust leak before the first O2 sensor.Most of the time, the best way to respond to a P0171 is to try cleaning the MAF sensor and the lines running to and from it. This will often resolve this issue.Next is change the oxygen sensor in bank one and closest to the engine.

Consult the manual that came with the scan tool to decode.

There is a Toyota TSB for a Computer malfunction.
There is a campaign for that, take it to your Dealer for repair, should be no charge

http://www.xcardiag.com/wholesale/high-quality-toyota-intelligent-tester2-it2-with-suzuki-47.html

This code reffers to a Mass air flow sensor or(MAF) Check the connections and /or replace it. Good luck.

No i would go for the o2 sensors ,two are fitted one before the cat and one after ,use universal ones now the 4 wire ones are 40euros each but the 3 wire ones are 90 euros each, in the box is a wire conversion colour code chart but basicly the two wires the smae colour go together either way around and the other two look at the conversion chart

What does that mean? Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.
Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.
Symptoms You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.
Causes A code P0171 may mean that one or more of the following has happened:

• 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.

P0171 - System Too Lean (Bank 1)
Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.

Symptoms: You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.

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

Possible solutions include:
* 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
* Inspect all vacuum and PCV hoses, replace if necessary
* Check for a dirty fuel filter and proper fuel pressure


Hope this helps (remember to rate this answer).

Did you erase the fault codes from the ecu computer, with the scanner, after the repairs were performed?

When the fuel trim is high teens or in the 20s then its the MAF that the problem. If fuel trim is normal, 2-5 then its the O2 sensor.

MAF-
Buy "Electrickleen" at the parts store.
Remove the MAF sensor, WHILE COLD, and blast the wire inside with cleaner.
The "hotwire" gets gummed up and changes the resistance of the wire so you get a bad input to the ecu and it trys to lean out for a rich condition that doesnt exsist.When it cant adjust anymore it trips the po171 code.

No need to replace the MAF. If it was bad, the check engine light would have come right back on as soon as you started the engine. The MAF not only measures the air going into the engine, but also measures the air temperature. Those 2 circuits are constantly sending info the the ECU. If either would fail, the ECU would light the check engine light. P0171 is a common code for incorrect readings (dirty) in the MAF. Cleaning it always helps, and cuts off the light. Your acceleration problem may be either a wrong Air-Fuel sensor (the one before the cat), or an "aftermarket" AF sensor. "Aftermarket" AF sensors have been shown to not work properly in Toyota vehicles. Hope this helps