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 your Engine Control Module (ECM) detects a lean fuel condition on Bank 2. 

How does that happen?
A lean fuel condition occurs if there’s too much air and insufficient fuel in your air fuel ratio (AFR). Usually, this means that your fuel system isn’t delivering enough fuel, and the fuel pressure is too low for the combustion process. 

Your Engine Control Module is designed to adjust your lean fuel condition when there’s too much air in your air fuel mixture — but only in small increments. 

If your air fuel mixture requires a higher compensation than usual, the ECM will trigger the check engine light and set code P0174. An example where this can happen is when a vacuum leak introduces unmetered air into the air fuel mixture.

Common Symptoms

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

If you have an active P0174 code, you may experience:

• Increased fuel consumption
• An illuminated check engine light
• Rough idle
• Engine misfires
• Engine coughing
• Decreased acceleration
• Engine stalling
• Low fuel pressure

Note: The P0174 code is very similar to code P0171. The P0171 code also indicates an issue with your airfuel mixture but refers to Bank 1.

Can I Still Drive?

Yes, you can still drive.

Generally, a lean code isn’t that serious. However, an intake leak in the inlet manifold 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 when the check engine light comes on and get this code fixed ASAP.

P0174 Causes

Below are some 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 weak 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
• A damaged intake manifold gasket
• Issues with the Engine Control Module (or Powertrain Control Module)

Diagnosis

Although you can diagnose the error code P0174 yourself, you’ll need specialized equipment to read fuel trim values, which are crucial for this repair job. Fuel trim values are what the engine control module uses to compensate for all problems relating to airfuel mixture ratios.

So, it’s best to let a professional mechanic handle the diagnosis for you, to avoid further damage.

Here’s how your mechanic will diagnose the problem:

1. First, your mechanic will analyze your short term fuel trim values, long term fuel trim values, and freeze frame data.

2. 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.

3. They’ll also inspect your air filter to ensure it’s not letting dust or debris clog up your MAF sensor.

4. Then, they’ll check your fuel system for issues, such as a weak fuel pump, by performing a fuel pressure regulator test.

5. They’ll also inspect your fuel injector and fuel filter components to see if they’re dirty or clogged.

6. Next, they’ll check if an intake leak in your intake system or vacuum lines allows particles to enter your engine.

7. Then, the mechanic will inspect your spark plug wells and rubber grommets for oil. Defective valve covers can also cause an oil leak.

8. They’ll check to see if your PCV valve and EGR valve are defective — allowing too much air into your air fuel mixture.

9. Finally, your mechanic will use a scan tool to test the air fuel ratio of your oxygen sensor (O2 sensor).

Your mechanic must complete the diagnostic process before attempting 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.

Note: Short term and long term fuel trim values help identify fuel system problems, such as a weak fuel pump, dirty fuel injector, low fuel pressure, intake manifold leak, etc. The short term fuel trim values measure immediate changes to your car’s oxygen levels, while long-term values measure O2 levels over a longer period.

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 they may perform:

➤ 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 the P0174 code.)

➤ MAF sensor issues: If it’s a mass air flow sensor problem, your mechanic will clean your mass airflow sensor with a MAF cleaner or replace the sensor if it’s broken. 

➤ Clogged air filter: A clogged air filter could contaminate 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: They’ll inspect your fuel system and fix problems such as a dirty fuel injector, weak fuel pump, 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, they’ll replace it with a new one.

Before a mechanic can reset the check engine light and fix code P0174, they’ll need about an hour to diagnose 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, they’ll give you a repair estimate.
Here’s what you can expect to pay depending on the issue:

• Vacuum leak repair: $150-$1000
• Cleaning a dirty MAF sensor: $40-$100
• Replacing a MAF sensor: $60-$385
• Fuel pump repair: $900 to $1,100
• Fuel pressure regulator repairs: $200-$550
• Exhaust repair: Up to $500 
• Air fuel sensor or oxygen sensor repair: $200-$500
• Valve cover gasket replacement: $100-$350
• Replacing a clogged fuel filter: $50-$150

Note: The repair costs above include labor charges.