P0174 – System too lean, bank 2
| Code | Fault Location | Probable Cause |
|---|---|---|
| P0174 | System too lean, bank 2 (Buy Part On Amazon) | Intake/exhaust leak, fuel pressure/pump, injector(s), AIR system, hose connection(s) |
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Table of Contents
- What Does Code P0174 Mean?
- What are the common causes of code P0174 ?
- What are the symptoms of code P0174 ?
- Codes Related to P0174
- Get Help with P0174
What Does Code P0174 Mean?
The long term fuel trim and the short term fuel trim provide essential diagnostic data for diagnosing engine problems. In fact, a scan tool reading of the long term fuel trim can lead to a quick fix of a P0174 or P0171 code.
Fuel trims are settings which control the amount of fuel entering the engine to achieve a stoichiometric ratio of 14.7:1. The stoichiometric ratio is the volume mixture of air and fuel that will result in complete combustion of the fuel and oxygen. The car’s computer control will always seek 14.7 liters of air for each liter of gasoline. It is important to remember this fundamental law for your car.
Since the stoichiometric ratio is very important to engine performance, there are multiple air sensors and fuel controls that measure the air and fuel entering your car’s engine. The most common sensors are the Mass Air Flow sensor (MAF), the Intake Air Temperature sensor (IAT), Manifold Air Pressure sensor (MAP), the Short Term Fuel Trim (STFT), the Long Term Fuel Trim (LTFT), and the Oxygen sensor (02). A few examples will explain the interaction of these sensors and their role in engine diagnosis.
What are the common causes of code P0174 ?
Unmetered air entering the engine is a common cause of the P0174 trouble code. While the air passing through the MAF sensor is metered by the car computer, intake leaks or vacuum leaks are not known. These sources of additional air increase the air to fuel mixture. A quick way to detect a leak is to observe the LTFT readings at idle and full throttle. At full throttle, a small leak will contribute far less air to the large overall volume of air entering the engine.
A lean condition, which can lead to the P0174 trouble code, is much more common than a rich condition. A lean condition is detected when the O2 sensor responds to the presence of oxygen by inhibiting its voltage output. Said another way, an oxygen sensor will produce an output of 1 Volt if the exhaust mixture does not contain oxygen. A typical 02 sensor reading for a lean condition will be much lower than 1 Volt as shown below.
When the car computer detects a lean condition in the O2 sensor, it will immediately try to correct the lean condition and return to the stoichiometric ratio by adding fuel. Enter your short term fuel trim (STFT). The short term fuel trim is a percentage change in fuel delivered to the engine. For a lean condition, more fuel is required, and the short term fuel trim will be positive anywhere between 0 and 50%. The short term fuel trim increases until the oxygen sensor tells the computer that the stoichiometric ratio of 14.7 exists. Once the engine is back in stoichiometric balance, the short term fuel trim will level out. Now enter your long term fuel trim (LTFT). The LTFT will be set at the STFT setting. The LTFT takes over for the STFT (which will return to zero after the LTFT memorizes the STFT setting) to keep the engine in stoichiometric ratio.
What causes the P0174 code? Generally, if the LTFT is above 25% for two driving cycles, the computer will throw the P0174 code.
What are the symptoms of code P0174 ?
The lean condition should disappear at full throttle, but be noticeable at idle if there is a small vacuum leak.
Codes Related to P0174
P0171 is the bank 1 version of this same code.
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Tengo un problema con el mismo código p0174 no sé que es le puse empaques nuevo de almicion sensor de oxigeno bomba de gasolina y cuando manejo todo va bien derrepente en pieza a desaselerar y no responde el aselerador pero no sé apaga y si aselero empieza a escuchar esplosiones en el motor
Translation:
I have a problem with the same code p0174 I don’t know what it is I put new starch gaskets oxygen sensor gasoline pump and when I drive everything goes well suddenly in a part to unwind and the accelerator does not respond but I don’t know it turns off and if the accelerator starts listening engine knocking
Hello Darvin. It sounds like it might be leaking from those gaskets you just had replaced. Another place vacuum could be leaking from is the EGR diaphragm. It would cause acceleration/ performance issues.
Replaced fuel filter, PVC valve, fuel injection pressure sensor, and cleaned the MAS. The P0171 and P0174 codes still appear. How do I determine the problem? The things that may be faulty are fuel injectors, O2 sensors, fuel pump…right? The runs with these, codes and acceleration is not a problem. I am thinking it is the injectors or O2 sensors that may be faulty.
Agreed with Nathaniel on this one. But one more thing: be ready to replace the MAF sensor with a factory unit. Have seen these codes come up with a bad MAF sensor, and still comes back after replacement because an aftermarket sensor was used. Let us know how it goes.
Hello, though these things you mentioned are normally the cause for this code. I have some personal experience with this issue. What I do know is it is running lean because of a loose or worn timing chain. Changing the injectors may help, but doing a timing chain and oil control valves will keep the codes from coming back. Best of luck.
hi does anyone know if this code would appear because I put a K&N air filter in?
Replaced my MAF sensor and the wire pigtail and began getting P0102 error code in my 2002 E39 BMW 530i indicating air flow sensor low circuit voltage. I figured this had to do with the but connected tictail I installed causing a voltage drop between the air sensor and ECU module therefore I removed the butt connector connection and soldered in another pig tail connector. However I continue to get the same error code. I am starting to believe possibly I have a faulty MAF sensor right out the box. Any advice or suggestions would be greatly appreciated, thanks in advance.
Rick Martin II
I received this code after installing a 1000 cm air intake….think it could be related? Hahahha
got this code after installing a coolant temperature sensor on 2005 kia sportage lx w/ 2.7l