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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... ran fuel pressure and seems to have the right numbers from the manual??? What else could it be????

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Running lean, try cleaning your MAF sensor, a dirty or faulty MAF will cause your engine to run lean. Cleaning the MAF with automotive electrical spray cleaner and see if that helps your issue.
What would really help you is to get a code scanner. Then you can clear the codes, and as soon as the CEL trips on, you can pull the code right away. That way you can get the first code(s) that shows up, which is usually the problematic code... if you continue to drive the vehicle with the CEL on and an air/fuel issue, it almost always causes additional 'chain reaction' codes to show, and those can be misleading to the root problem.

Again, I would clean the MAF, then reset the ECU ( do it with my code reader, or you can disconnect the battery for a few moments, too). Then, when the first code pops up, scan for it. That'll point you in the right direction.

Thank you for using fixya and keep me posted.

Posted on Apr 27, 2010

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Posted on Jan 02, 2017

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Failed emissions with 2001 BMW 325i. Codes given were P0313, P0171 System too lean Bank 1, and P0174 System too lean bank 2. What do these codes mean?


Those codes mean the fuel to air ratio is to lean, not enough fuel. This is caused by quite a few things, most common is a intake manifold vacuum leak or other source (like hoses and the brake booster) A problem with the MAF (mass air flow) sensor can cause this as well if it is reading the incoming air volume wrong.

Feb 27, 2017 | 2001 BMW 325i

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Code P0171


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

Dec 01, 2015 | 2004 Nissan Titan

1 Answer

What does code system to lean bank 1 mean on my 2000 lexus rx300


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.

Apr 10, 2014 | 2000 Lexus RX 300

1 Answer

4 Codes in computer


code p0128 indicates a mechanical fault ( could be the thermostat stuck open)
code p0174 -system too lean -bank2 ===causes --intake /exhaust leak--fuel pressure/pump--injectors--AIR system--hose connection/s
code po171 refers to system too lean bank 1 same as po174 with the HO2S sensor being the culprit. As to all being related . only by way of the o2 sensors
code p0442 is not connected to the first 3 as it is in a different section of the fuel system

Apr 09, 2014 | 2003 Saturn VUE

1 Answer

Dakota p0171 p0174 taurus


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.

Sep 06, 2013 | 2009 Citroen C8 2.0

1 Answer

My lexus rx300 2001 is blowing white smoke and reading codes p0171 and p0174


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.

Feb 22, 2012 | 2001 Lexus RX 300

1 Answer

HOW TO FIX CODES 171 AND 174


fault code p0171 is system too lean bank 1.................. intake/exhaust leak. air system MAF/VAF sensor. Fuel pressure/pump , injectors HOS2.

fault code p0174 is system too lean bank 2...................intake exhaust leak, fuel pressure/pump , injector(s) Air system, Hose connectors

hope this helps you

Jan 07, 2012 | 1999 Ford Ranger SuperCab

1 Answer

P0171 and P0174 Left and Right bank lean trouble codes pulled from ECU. Check Engine Light illuminated.


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).

Feb 26, 2011 | 2008 Hyundai Entourage

1 Answer

I have a code reader and the code is P0171 P0174 System too lean. what makes the system too lean?


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.

Jan 16, 2011 | 2000 Ford Explorer

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