My lexus rx300 reads codes p0171 and p0174 system lean on bank 1 and two I have fixed both air fuel ratio sensors and the fuel pump/filter all brand new... ALSO RAN THE FUEL PRESSURE AND ALL READ PERFECT WHAT DO I DO???? IM GOING CRAZY!!!!

Question edited for clarity. It is P-Zero 0, not P-oh O.
Please always include 'year make model' first 3 words, or it it is difficult to answer and some vehicles are slightly different or more precise and will show known issues.

P0174 - OBD-II Trouble Code Fuel System Too Lean (Bank 2)

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When a vehicle has the fault code P0174, it means that computer can no longer automatically adjust the mixture between air and fuel. Code P0174 applies to V ...

P0174 OBD-II Trouble Code: System Too Lean (Bank 2)

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Code P0174 indicates that there is a lean condition detected by the Engine Control Module (ECM). A lean condition will be created if there is too much air, and ...

P0151 Code - What Does It Mean & How To Fix It - OBD2PROS

https://obd2pros.com > dtc-codes > p0151
A P0151 code is caused by an ECM (Engine Control Module) receiving a signal indicating the O2 sensor for bank 2 sensor 1 has failed to increase the voltage ...

Code P0171 - System Too Lean: Symptoms, causes, common ...

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Jul 10, 2021 - The OBDII trouble code P0171 - System Too Lean (Bank 1) means that the engine air-fuel mixture is too lean, or there is too much air and too ...

System Too Lean P0171
Clean the MAF sensor and IAC valve with MAF cleaner
Inspect all vacuum and PCV hoses, replace/repair as required.
Inspect all hoses and connections in the air intake system.
Inspect and/or test the intake manifold gaskets for leakage.
Check for a dirty fuel filter and proper fuel pressure.

As a last resort, replace O2 sensor

System Too Lean P0174
Error code P0174 is described as System Too Lean (Bank 2). This means there is incorrect ratio of air and fuel on the car's engine system, specifically on Bank 2 of the Cylinder. “Too Lean” means there is too much oxygen in the exhaust.

As a last resort, replace O2 sensor

code p 0171 refers to system too lean bank 1===causes ---intake /exhaust leak---AIR system----MAF/VAF sensor---fuel pressure/pump---injectors/s--- heated oxygen sensor (HO2S in the exhaust manifold before the cat converter)
for this code the most likely fault will be the HO2S unit as it reads the exhaust gas composition and reports to the ECM so that the air/fuel ratio can be corrected
code p 0174 refers to system too lean bank 2===causes -same as for p 0171
fuel trim is what the ECM does after it receives an constant flow of information from all of the sensors and it alters the air / fuel ratio for the new parameters
you will have noticed a change in engine performance and fuel economy when driving at a constant speed over a distance or conversely a loss of economy when reverting to city driving
It also explains the advertised fuel economy figures --one for city driving and a better figure for highway driving

P0171 - System Too Lean Bank 1 Share
1 ' Add Comment Possible causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection
What does this mean? Tech notes
If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.
What does this mean? When is the code detected?
- Fuel injection system does not operate properly.
- The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Excessive Fuel Consumption
P0171 Description
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECM judges the condition as the fuel injection system malfunction and light up the Malfunction Indicator Light (MIL) (2 trip detection logic).
Read more: http://www.autocodes.com/p0171.html#ixzz3t65yA9xI

Try this cheap fix

It could be caused by many things, but generally it means that your engine is running too lean - usually indicating a vacuum leak. It could also be that the O2 sensor is bad and giving a false reading.

code p0171 refers to system to lean bank 1==causes intake /exhaust leak--AIR system--MAP/MAF sensor--fuel pressure/pump--injectors--HO2s Have a fuel pressure test done on the fuel manifold to check for blocked filter/faulty pump/fuel pressure regulator faults
code p0174 refers to system to lean bank 2 --same causes including hose connection/s
code p0420 refers to catalytic converter system -bank 1 efficiency below threshold==causes catalytic converter--wiring--HO23. Check the cat converter is not cracked inside and the oxygen sensor is working.

Hi there:
P0171 - System Too Lean (Bank 1)
P0174 - System Too Lean (Bank 2)
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.

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.

A code P0171 or P0174 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.

P0171 = system too lean bank 1
P0174 = system too lean bank 2

The fuel/air mixture is too lean for the entire engine. The fuel pump pressure could be too low. The fuel pump pressure regulator could be at fault. There could be an air leak downstream of the MAF sensor. MAF sensor (hot wire type) could be dirty. Check for intake manifold vacuum leaks. The engine coolant temp sensor and/or the intake air temp sensor could be faulty (stuck at full hot mode).

P0171 - Fuel Injection System Too Lean Bank 1
Possible Causes:
- Intake air leaks
- Front Heated oxygen sensor may be faulty
- Injectors may be faulty
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Mass air flow sensor may be faulty
- Incorrect PCV hose connection

P0174 - Fuel Injection System Too Lean Bank 2
Possible Causes:
- Intake air leaks
- Front Heated oxygen sensor may be faulty
- Injectors may be faulty
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Mass air flow sensor may be faulty
- Incorrect PCV hose connection

What Causes These Codes: Fuel injection system does not operate properly. The amount of mixture ratio compensation is too large. (The mixture ratio is too rich.) The Powertrain Control Module (PCM) monitors the engine Air/Fuel mixture ratio, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The PCM calculates the necessary compensation to correct the offset between the actual and the theoretical ratios. In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the PCM judges the condition as the fuel injection system malfunction and light up the engine light. The codes is usually set when there is an intake leak after the air flow meter, before replacing any parts check for loose or broken hoses and intake gasket leak. On Ford some models dirty air filter, and dirty or faulty air flow sensor are the cause of the problem.