Error Code P0171: System too Lean (Bank 1)
What it means is that the engine is running lean. There are many
possible problems that may cause the air-fuel mixture to be lean:
Defective or contaminated airflow sensor, intake vacuum leak, dirty
fuel filter, etc.
There are certain tests to be performed to find the
exact cause of the problem. Common problems with some engines are
defective airflow sensors and vacuum leaks.
The Oxygen Sensor is located under hood, center, front engine area, above exhaust
pipe flange, mounted in exhaust manifold
.Heated oxygen sensor (Bank 1, Sensor 1)-5S-FE engine except California
Heated oxygen sensor (Bank 1, Sensor 2)-5S-FE engine except California
The oxygen sensor can be located in several places. Either in the exhaust manifold, front pipe or catalytic converter.
WARNING
Care should be used during the removal of the oxygen sensor. Both the sensor and its wire can be easily damaged.
The Mass Air Flow Meter (MAF) contains a spring-loaded measuring plate
or cone. The plate/cone is connected to a potentiometer which controls
the signal to the ECM. In this way, the control unit is advised of
intake air volume and can control injector duration and ignition
advance accordingly. All engines except the 5S-FE engine uses an air
flow meter. The 5S-FE engines uses a Manifold Air Pressure (MAP) sensor.
Test the resistance of terminals E2 (1) and THA (2) of the MAF sensor-1MZ-FE engine
Mass Air Flow (MAF) meter resistance. If the readings you observe are out of the specified range, replace the MAF meter-1MZ-FE
View of the Manifold Absolute Pressure (MAP) sensor and its related components:
Replacing the MAP sensor simply requires unplugging the vacuum and
electrical connections, then unbolting the sensor. Inspect the vacuum
hose over its entire length for any signs of cracking or splitting. The
slightest leak can cause false messages to be send to the ECM.
I hope helps with this.