Home TroubleshootingOBD Codes P0174 – Is Your Engine Running Too Lean (And How To Fix It)?

P0174 – Is Your Engine Running Too Lean (And How To Fix It)?

by Kelvin Yates

A P0174 error code indicates that bank 2 of your engine is running lean. Running lean signifies that too much air and insufficient fuel are pumped through the chambers.  On the contrary, running rich ensues when there is too much gas and not enough air.

Your engine block’s side without cylinder number one is known as bank 2. It depends on your manufacturer whether this bank is on your car’s driving or passenger side. To locate it under your hood, consult your user manual. Keep reading to learn all about the P0174 code.

Lean And Rich Engine Codes

The O2 sensor, the ECM/PCM, and other components all work to maintain equilibrium in the combustion chamber. If the mixture wanders too far out of balance, a rich or lean code is stored in the process. Then the ECM/PCM’s fuel trim strategy adjusts the injector pulse width. This is to move the mixture in the opposite direction to balance the air/fuel mixture.

It should be emphasized that the oxygen sensor is intended to detect oxygen rather than fuel. Since it could care less about unburned gasoline in the exhaust stream. Because of this, anytime a cylinder misfires due to spark or compression, unburned fuel in the exhaust stream and the oxygen that did not combine with that fuel will both pass the O2 sensor.


But all that the sensor will detect is oxygen. If so, a P0174 code might not signify a lean situation. This is especially if other codes for misfires are present as well.

If the air/fuel ratio isn’t balanced and there is too much air, oxygen molecules will be left over after the combustion process. These will make their way into the exhaust. In other words, too much air and not enough fuel are considered lean. But the O2 sensor can’t even smell fuel and doesn’t know it’s there in the case of a misfire.

P0174 Code

A P0174 error code means that either too much air or not enough gasoline is entering your engine block’s second bank. As a result, the air-to-fuel ratio inside the engine is off. The ideal air-fuel ratio for the majority of automobiles is 14.7 parts air to 1 part gasoline.

When your car saves the code P0174, it signifies that there is a significant difference between the amount of gas and air entering the engine. This means that your fuel injectors are unable to permanently correct the issue. There is a bigger problem at hand than a small increase in gasoline can handle.

When your car’s powertrain control module (PCM) notices that the air-to-fuel ratio is too lean, a P0174 code is set. This indicates that the PCM is signaling that the engine is burning not enough fuel while receiving too much air into the combustion chamber.

The oxygen sensors in the engine bay of your car provide data to the PCM. The PCM then continuously adjusts the amount of fuel and air in the engine to match the values from these sensors. The PCM will set the P0174 code when the specified factory range deviates from the specification. This also happens when there is less gasoline present than the engine requires.

The PCM then instructs the fuel injectors to inject extra fuel into the engine’s combustion chamber. Fuel trim is what this action is known as, and in the instance of the P0174 error code, where extra fuel is required, this is a positive fuel trim.

P0174 System Too Lean Bank 2

The fact that the P0174 and associated codes distinguish between problems with the air-to-fuel ratio in bank 1 and bank 2 is another crucial point to remember. The #1 cylinder is located on bank 1 of the engine, whereas the #2 cylinder is located on bank 2.


When the PCM can no longer correct the low fuel condition by injecting fuel, the P0174 code is set. Followed by this, a check engine light will also illuminate. It’s crucial to remember that this code usually always pairs with at least the P0170 code, which merely indicates that a fuel trim anomaly has been found.

Even if you encounter the P0172 code, which denotes the opposite of the P0174 code, the P0170 code again could be activated. The PCM detects a negative fuel trim and requests that less gasoline be injected through the fuel injectors, which sets off the code. This denotes a “too rich” engine operation.

Bank 2 refers to the side of the engine block that houses the #2 cylinder and is normally only present in engines like V6s, V8s, or V10s. But some in-line 4 engines also divide into bank 1 and bank 2, and they identify their cylinders in the same way.

Finally, whether bank 2 is on the driver’s or passenger’s side depends on the make and model of your car. In order to determine precisely what kind of fuel trim issue is occurring and where it is in the engine block, codes P0170 through P0175 are used.

P0171 And P0174

The fault codes that appear in lean scenarios are P0171 and P0174. A lean condition in cylinder bank 1 initiates the P0171 code, and a lean condition in cylinder bank 2 initiates the P0174 code.

Even while it can recover a lean condition, the Engine/Powertrain Control Module (ECM/PCM) can only do so to a limited point. To alert the user to the need to resolve this issue, the ECM/PCM records the P0174 code. To find out more, check out our guide on the P0171 Toyota or P0171 Nissan code.

P0174 Causes

Unmetered air entering the combustion chamber is the most frequent cause of the P0174 error codes. The majority of the time, poor fuel pumps or faulty or unclean mass airflow sensors are to blame for this. Unmetered air may potentially enter the system through clogged or dirty fuel filters or fuel injectors, setting any of these errors.


Engine running lean or rich must also be investigated as a result of defective oxygen sensors. The sensor might occasionally be defective. However, the most typical cause is a vacuum leak or a fuel pump issue. A P0174 code and its associated problems might also be caused by exhaust leaks in your car.

A vacuum system leak or crack will let extra airflow into the engine. When your automobile displays the P0174 code, the leak may also be in the PCV line, or it may be at the joint where the vacuum pipes connect to the PCV valve.

Fuel injectors or fuel pumps are the sources of low fuel levels. The engine won’t receive enough gasoline if the fuel pump is inefficient or weak. Similarly, if your fuel injectors are broken or clogged, they cannot maintain the proper air-to-gas ratio. The proper amount of gas cannot enter the engine due to a clogged fuel filter.

You should examine the sensors if your vacuum system is leak-free and if you are confident that your engine is receiving enough gasoline. The mass airflow sensor, oxygen sensor, or air-fuel ratio sensor may all be malfunctioning. The following are some of the causes that might have resulted in a P0174 Code-

  • A clogged or damaged mass airflow sensor
  • Vacuum leaks
  • Faulty fuel pump
  • Filthy or clogged fuel injectors
  • Fuel filter clog
  • Exhaust leak
  • Faulty oxygen sensor
  • Faulty air-fuel ratio sensor

Vaccum Leaks And MAF Sensor Issues

This problem could arise from a variety of small or large repairs. To find the root of your error code, start with the simplest problems and work your way up. Air entering the system in an unobservable location is a common source of a lean condition.

There are two primary causes of this: a vacuum leak in the intake system – a faulty MAF sensor, or an issue with the intake system itself. Start by inspecting the intake boot that connects the throttle body to the MAF. Check for cracks, hose clamps that are loose, and other potential air entry points.

Next, look for cracks or fractures in all of the vacuum hoses on the engine. When the engine is running, pay close attention to what you hear. Because occasionally the sound of air being pulled through a break indicates a significant vacuum leak. Look for leaks or cracks in all of the hoses that are part of the PCV system.

There could be other serious problems if nothing here comes up. One is a vacuum leak brought on by a damaged throttle body or intake manifold gasket. This will result in a significant vacuum leak and start a lean situation.

Improper fueling is another potential problem that may be brought on by low fuel pressure (perhaps from a fuel pressure regulator, a blocked pump strainer in the tank, or a weak pump), or by weak, plugged, or malfunctioning fuel injectors. It’s crucial to remember that fuel problems like these frequently result in misfire codes as well, either randomly or on specific cylinders.

Can You Drive With P0174 Code

The seriousness of the P0174 code and its associated codes can vary. The code doesn’t pose any immediate risks by itself. But you should have it examined right away by a trained technician. The PCM may sustain more damage that would be more expensive to fix if the code were to stay there for a longer time.

However, most modern cars will take corrective action by switching to “limp mode” or restricted power mode. This is done in order to prevent the engine from suffering significant damage. As we’ve previously mentioned, operating a vehicle under lean conditions might result in spark knocking or pinging. This can result in more dangerous repercussions.

Pinging occurs when oxygen (O2) is changed into nitric oxide (NOx), a pollutant of the atmosphere. And as a result of this action, both the valve surfaces and your combustion chamber may sustain damage. As a result, the catalytic converter overheats to the point where it flashes brightly red. This condition threatens to set other components of the automobile on fire.


If the P0174 or any of its associated codes are displayed on your dash, you will be physically able to drive, but it is not advised. If your car does enter limp mode or reduced power mode, this is additional evidence that the problem is more serious than you realize and you should have it checked out by a professional mechanic right away.

P0174 Symptoms

Even if no symptoms are apparent right away, it is still possible that the car is running too lean and compromising its fuel efficiency. If the wrong air-to-fuel ratio is repeatedly pushed into the system due to a problem with your fuel pump or injectors, this might result in long-term damage.

The ratios that are predetermined at the factory for engine functioning are there for a reason. They have been tested and are what is required to keep the vehicle running more smoothly for a longer period of time.

A common P0174 code symptom is that the engine seems to be running weakly and could stall at any moment. The engine can no longer sustain a constant idle when you stop at a stoplight, which is when the stalling frequently happens.

However, if the problem is brought on by a vacuum leak, you can hear a hissing sound emanating from your engine compartment. It’s possible that your engine has trouble starting because the combustion chamber isn’t receiving enough fuel.

Additionally, you can experience a loss of power. This happens as a result of even less fuel getting to the engine’s combustion chamber. You could also endure an engine knocking or pinging when the engine is under load or when going up a hill. The following are also some symptoms of the P0174 code-

  • Check Engine Light is on
  • Lack of power
  • Rough idle
  • Rough start up
  • Engine knocking
  • Engine misfiring


In addition to impairing engine performance, the issues that result in the trouble code P0174 over time may also harm other components. For instance, they can damage the catalytic converter because misfires let raw fuel into the catalytic converter.

Dust particles can eventually harm cylinder walls. This happens if unmetered or unfiltered air is flowing via the intake manifold or air ducts. You surely want to avoid this costly repair.

Your issue might be resolved with a straightforward task like removing a clogged fuel filter or cleaning the MAF sensor. However, putting off the issue could lead to an expensive repair in the future. Cleaning a sensor or changing a filter is less expensive than replacing a catalytic converter and other damaged parts.

The first step in diagnosing and resolving a P0174 code, or any of its related codes, is to let a certified technician handle any fuel system repairs. They will want to confirm that the fuel pressure, fuel injector pulse, fuel injector functionality, and clog-free status are all where they should be.

They will also inspect your fuel lines for damage before checking your vacuum lines for leakage. Any issues you find should be fixed because these leaks result in air escaping rather than entering the engine’s combustion chambers.

The mass airflow sensor should then be disconnected, cleaned, and then reconnected. DIY enthusiasts shouldn’t undertake steps like these; they should only be performed by expert technicians. You should rerun the diagnostic test after reconnecting to see if the P0174 error code or any related errors are present.

The exhaust should be checked for leaks, and any necessary system repairs should be made with professional assistance. If the issues continue, you might want to think about changing both the oxygen and air-to-fuel sensors to solve the problem.

Repair Cost

When diagnosing P0174, it’s crucial to finish the entire diagnostic procedure. The O2 or A/F sensor will read differently to make up for a dirty or malfunctioning mass airflow sensor or a vacuum leak.

However, many people will replace the air/fuel sensor or O2 sensor as soon as they get a bad reading. The key to correctly diagnosing P0174 is reading and examining the freeze frame data as well as the fuel trims.

Most repair shops will begin with an hour of “drag time” if you bring your car in for a diagnosis. This is the time spent in labor diagnosing your specific issue. This normally costs between $75 and $150, depending on the labor rate at the shop.

If you hire the shop to handle the repairs, many, if not most, will deduct this diagnosis price from any necessary work. A shop will then be able to provide you with an accurate estimate for repairs to resolve your P0174 error.

One or more of the following repairs may be required to address the underlying problem when dealing with the P0174 code. The estimated cost of repair includes both the cost of the necessary parts and the cost of the labor needed to complete each potential repair. The following are the cost of repairing or replacing various components that might be the root of the issue-

  • Vacuum leak: $100-$200
  • Clean MAF: $100
  • Replace MAF: $300
  • Fuel pump: $1300-$1700
  • Fuel pressure regulator: $200-$400
  • Exhaust repair: $100-$200 (if welded to repair)
  • Air fuel sensor or oxygen sensor: $200-$300

P0174 Ford

Ford’s P0171 and P0174 lean codes correspond to the first and second cylinder banks, respectively. These codes are frequently set in various Ford cars when the powertrain control module (PCM) detects an excessively lean air/fuel combination (too much air, not enough fuel).

If a code reader for car or scan equipment is put into the vehicle diagnostic port when the check engine light is illuminated, one of these codes—or both—may be discovered. If the car is driven for a sufficient amount of time, both codes will usually be set.

Ford vehicles with a transverse-mounted V6 engine and front-wheel drive will display a P0174 lean code for bank 2, which is the cylinder bank on the left (driver) side of the engine. On engines with four cylinders, this code is not set (no bank 2).

Intake leaks or the intake plenum gasket and seals are most likely to blame for the issue if the P0174 and P0171 codes are present together. The next step is to change the air filter and clean the airflow meter if there are no intake leaks. The front oxygen (O2) sensor may need to be changed if the issue continues.

P0174 Nissan

The P0174 error code is among the most often encountered ones for the Nissan Maxima. When the fuel injection system on a Nissan Maxima isn’t working properly, the P0174 code is frequently set. Typically, a lean engine condition will set off the code.

P0174 often doesn’t cause any drivability problems. The “service engine soon” light turning on is typically for most folks the first indication that anything is wrong at all.

P0174 Chevy Silverado

Incorrect fuel injection operation frequently results in the Chevy Silverado throwing the P0174 code. Typically, a lean engine condition will set off the code. P0174 often doesn’t cause any drivability problems. The “service engine soon” light turning on is typically for most folks the first indication that something is wrong.

Final Conclusion

A P0174 error code may represent a serious problem. Running your engine in a lean condition will result in additional issues even if the underlying cause itself is not urgent. If you don’t take early action to correct the situation, future damages could be far more severe and expensive.

You run the risk of having an overheated engine if the problem is not fixed. You face the risk of a blown head gasket, warped cylinders, or other issues that make it hard to drive if you let your car run hot for an extended period of time. Remember that an OBD-II code P0174 indicates a significant problem that requires your immediate attention.

Frequently Asked Questions

What Causes P0171 And P0174 Codes

The most common cause of the P0171 and P0174 codes is a vacuum leak. These codes are set by the car’s computer when it notices too much oxygen in the exhaust. Excessive oxygen readings and less-than-enough fuel burning result in these lean codes.

How Do I Fix Code P0174

First, the sensors should be thoroughly cleaned and tested for functionality. Followed by this, all of your hoses and intake should be inspected. The next step is to do a vacuum test on the running engine. You can utilize a vacuum diagnostic gauge or enlist the aid of a qualified shop at this point.

How Do I Fix Code P0171 And P0174

Focus on the parts that affect all cylinders, such as a MAF sensor, and a blocked fuel filter. Also, check for problems with a fuel pressure regulator if your computer logs both the P0171 and P0174 codes. Otherwise, focus on the specific side of the engine that your diagnostic trouble code represents.

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