P0174: System Too Lean on Bank 2

What is P0174?

Error code P0174 is an OBD-II diagnostic trouble code defined as “System Too Lean (Bank 2).”

It indicates via a lit check engine light that a lean fuel condition is detected by your Engine Control Module (ECM) on Bank 2. 

A lean fuel condition is created if there’s too much air and not enough fuel in your air fuel ratio (AFR). Usually, this means that your fuel system isn’t delivering enough fuel for the combustion process.

Your Engine Control Module (or Powertrain Control Module) is designed to adjust your lean fuel condition back to normal when there’s too much air in your air fuel mixture, but only in small increments. 

If your air fuel mixture requires greater compensation than normal, code P0174 may be set.

Common symptoms

Many of the symptoms associated with error code P0174 are more noticeable at lower speeds and revolutions per minute (RPM).

If you have an active P0174 code, you may experience one or more of these common symptoms:

• Increased fuel consumption
• An illuminated check engine light
• A rough or high engine idle
• Engine misfires
• Engine coughing
• Decreased acceleration
• Engine stalling

Note: Lean code P0174 code is very similar to code P0171. The P0171 code also indicates a lean fuel condition but refers to Bank 1.

Can I still drive?

Yes, you can still drive.

Generally, a lean code isn’t that serious. However, a leak in the air intake can let particles enter the engine and cause internal damage. Furthermore, a lean fuel condition can lead to friction between some of the moving parts in your engine and damage critical components.

So, it’s best to head to a professional mechanic and get this code fixed ASAP.

P0174 causes

Here are some of the most common causes of the error code P0174:

• A vacuum leak due to a damaged intake manifold gasket or a punctured vacuum hose
• A malfunctioning mass airflow sensor (MAF sensor)
• A clogged fuel filter or failing fuel pump
• A clogged or dirty fuel injector
• A failing fuel pressure regulator 
• An exhaust leak
• A cracked throttle body gasket
• A damaged O2 sensor 
• A worn-out spark plug
• Issues with the Engine Control Module or Powertrain Control Module

Diagnosis

Although you can diagnose error code P0174 yourself, there’s some specialized equipment needed for this repair job. So, it’s best to let a professional mechanic handle the diagnosis for you, to avoid doing any more damage to your car.

Here’s how your mechanic will diagnose the problem:

• First, your mechanic will analyze your long term fuel trim values and freeze frame data.
• If you have a dirty MAF sensor, the fuel trim values will increase as your engine speed increases. So, your mechanic will use a scan tool to test your mass air flow sensor.
• They’ll also inspect your air filter to ensure it’s not letting dust or debris clog up your MAF sensor.
• Then, they’ll check your fuel system for issues by performing a fuel pressure regulator test. 
• They’ll also inspect your fuel injectors and fuel filters to see if they’re dirty or clogged.
• Next, they’ll check if there’s a leak in your intake system or vacuum lines allowing particles to enter your engine.
• Then, they’ll inspect your spark plug wells and rubber grommets for oil. An oil leak can be caused by defective valve covers. 
• They’ll check to see if your PCV valve and EGR valve are defective — allowing too much air into your air fuel mixture.
• Finally, your mechanic will use a scan tool to test the air fuel ratio of your oxygen sensor (O2 sensor).

Note: It’s important for your mechanic to complete the entire diagnostic process before attempting any repairs. You don’t want to pay for a new MAF sensor when your O2 sensor is the root cause of the lean fuel condition.

Possible repairs for P0174 & Costs

Since several different issues can cause lean code P0174, there isn’t just one possible solution. 

Once your mechanic has diagnosed the problem, here are some of the common fixes:

• Check for other error codes: Your mechanic will use a scan tool to ensure no other error codes indicate problems (that may or may not be related to P0174.)
• MAF sensor issues: If it’s a mass air flow sensor problem, your mechanic will clean your mass air flow sensor with a MAF cleaner or replace the sensor if it’s broken. 
• Clogged air filter: A clogged air filter could be dirtying your MAF sensor, so your mechanic will clear it out if needed.
• Faulty oxygen sensor: Your mechanic will replace your O2 sensor if it’s defective.
• Fuel system issues: Your mechanic will inspect your fuel system and fix problems such as a dirty fuel injector or clogged fuel filter. 
• Vacuum leak: If there’s a vacuum leak, your mechanic will inspect your vacuum hose or intake manifold gasket and replace them if needed.
• Faulty EGR valve or PCV valve: If there’s still too much air causing a lean fuel mixture, your mechanic will replace your EGR valve and PCV valve.
• Defective valve cover gasket: Finally, if there’s an oil leak due to a damaged valve cover gasket, your mechanic will replace it with a new one.

Before a mechanic can fix error code P0174, they’ll need about an hour of diagnosing time to determine the problem. Depending on where you live and the labor costs in your area, you can expect to pay $75-$150 for this service.

Once your mechanic has diagnosed the issue, the auto repair shop will give you a repair estimate.

Here’s what you can expect to pay depending on the issue:

• Vacuum leak repair: $100-$200
• Cleaning a dirty MAF sensor: $100
• Replacing a MAF sensor: $300
• Fuel pump repair: $1300-$1700
• Fuel pressure regulator repairs: $200-$400
• Exhaust repair: $100-$200 
• Air fuel sensor or oxygen sensor repair: $200-$300
• Valve cover gasket replacement: $150-$400

Note: The repair costs above include labor charges.