P0174 Diagnostic Trouble Codes: System Lean Bank 2

Car engines have several car sensors and system components that work together for efficient performance. Unfortunately, they do not need a one-time tuning to run efficiently forever. Instead, they need frequent adjustments for optimal performance. And the sensors and the car computer make these small adjustments to maintain optimal performance. 

However, these systems cannot correct all problems. When the impending issue is bigger than what the powertrain control module can handle, it’ll trigger a check engine light on the dashboard and throw a fault code. By this, the driver will know there is an underlying problem that needs attention.

If the engine stores a P0174 error code, it means there is too much air or too little fuel in the bank 2 cylinders. This situation is called ‘engine running lean,’ and the opposite is engine running rich. 

This article will examine causes, symptoms, diagnostics mistakes, and how to fix and diagnose error P0174 on BMW and other car models. But, first, let’s see what this error code means.

p0174 code

What does error code p0174 mean?

Diagnostic trouble code P0174 means system too lean bank 2. This means the powertrain control module (PCM) has detected lean conditions in bank 2 in the air-fuel ratio (AFR). Lean conditions mean there is too much air or too little fuel.

Bank here means the location of the cylinder head in v-type engines. Check out this article, bank 1 and bank 2 locations, to understand what we mean by bank 2. This will help you stay on the same page as we progress along.

Auto manufacturers design car computers to easily adjust rich and lean conditions to the designated air-fuel mixture ratio. However, the computer can only adjust a lean condition accurately only when the offset is very small.

If the air-fuel mixture ratio offset is too much for the car computer to adjust, the ECM will throw an error code P0174 on Ford or whatever vehicle you have. Once this happens, the car computer will display an engine warning light to notify the driver of an impending issue that needs attention.

It is essential to note that the P0174 and P0171 mean lean conditions. The only difference is that the P0171 means too much air or too little fuel in bank 1, while P0174 means too little fuel or too much air in bank 2.

What is the symptom of error code p0174?

The P0174 diagnostic trouble codes will display several warnings to notify the driver of underlying issues in the system. Below are the symptoms to watch out for.

Check engine light

Like several electrical and mechanical issues in a vehicle, the car computer will display an engine warning light on the dashboard. A responsible driver should always pay attention to the dashboard when driving.

The car computer constantly triggers several lights on the dashboard whenever it detects any fault. Check engine light is the most discussed warning light because the powertrain control module can trigger it for several reasons. Therefore, do not conclude your engine is running lean without proper diagnosis.

Rough idle

Another common sign of a lean engine is rough idle. Manufacturers design engines to run at a specific air-fuel ratio. If there’s an offset from the designated ratio, the engine will suffer when running or idling.

Once an engine is running lean, the vehicle will run rough, especially on idle. However, the roughness on idle depends on the severity of the offset.

Poor acceleration

When an engine does not receive the required fuel for a proper combustion process, the vehicle will suffer poor acceleration. As a result, the gas pedal may feel unresponsive overtaking a vehicle when driving uphill.

Engine stalling and misfiring

A vehicle can misfire for several reasons. A primary cause for engine misfiring is improper air-fuel mixture ratio. A P0174 on Toyota and other car models can cause engine misfiring. However, you’ll mostly notice it when carrying a load and accelerating.

Engine stalling and misfiring will lead to sluggish or slow acceleration, and you’ll find it difficult to maintain a certain high-speed level.

Loss of engine power

If you experience a loss of engine power while driving, it shows the engine is running with less fuel or too much air. So, a car running lean can also cause engine hesitation when driving.

Engine sputtering

Engine sputtering is a clear and unnerving situation that shows something is wrong with the fuel system. If your vehicle’s engine sputters, it means the engine is about to run out of gas or has a lean condition. Sometimes, it may feel like the engine is coughing.

What Causes error code P0174

Several factors can cause the car computer to register a P0174 error code. For example, since the P0174 means the engine is running lean, one or more fuel system components or the air filtration systems may be bad. Here are common causes of P0174 fault codes you should watch out for.

The most common cause of error code P0174 is a vacuum leak. When unmeasured air is introduced into the air-fuel mixture, it’ll make the car computer throw P0174 fault codes. The unmeasured air can stem from vacuum lines, PCV hoses, and intake manifold gasket.

Other probable causes include;

  • Clogged fuel filter
  • Bad fuel pump
  • Dirty or lousy bad mass airflow (MAF) sensor
  • Dirty or clogged fuel injectors
  • Exhaust leak
  • Faulty oxygen sensor
  • Faulty air-fuel ratio sensor
  • Malfunctioning powertrain control module (Not likely the case, though possible).

p0174 system too lean bank 1

How serious error code p0174 is?

A P0174 on Lexus or any car model is a moderate case. However, it’s important to note that leaks from the intake systems can allow particles to enter inside the engine. This can cause catastrophic damages if not fixed as soon as possible.

Common P0174 diagnosis mistakes

Though diagnosing a P0174 code bank 2 can be challenging and time-consuming, mechanics often add to these issues by making some diagnostics mistakes. For example, a common diagnostic mistake of P0174 is replacing suspected parts without proving them to be bad through testing. Another mistake is not checking the intake hoses and lines for leaks.

How do you fix P0174?

If you’re asking, how do I fix the P0174 error code? Here are the possible repair approaches to fix the P0174 on Ford F150. Of course, this will also fix the issues on several other vehicles.

How to diagnose

This is the right guide if you’re a DIYer who wants to diagnose and fix the P0174 error code at home. You’ll need common hand tools and a diagnostic machine for a proper diagnosis. Before we go ahead, kindly note the P0174 fault is an intermediate repair. For your information, it is not a beginner task.

Tools and Items Needed

  • Scan tool
  • Screwdriver
  • Pressure testing gauge
  • Pliers
  • Soapy water
  • Mass air flow cleaner
  • Vehicle-specific repair manual

Step 1: Scan the vehicle

Grab your scan tool and locate the OBD port on your car. Next, plug in the scanner and pull out all the codes in the memory. If there are additional codes in your vehicle memory, fix them before continuing to the next step.

Step 2: Examine all the vacuum lines

Once you have ascertained there are no other codes on the vehicle memory, examine the vacuum lines for leaks. A vacuum leak will make a hissing sound in that area. However, it could be challenging to hear the hissing sound while the engine is running.

If you can’t hear or trace the hissing sound, pour soapy water into the spraying can and spray it on the hissing area. This will make it easier to track the leak. Next, spray the soapy water on the vacuum lines. The engine will stall or sputter once you spray it on the leaking lines.

Step 3: Examine the EGR, PCV, and MAF sensors

Examine the Oxygen sensor and clean it with mass air flow or contact cleaner. After that, inspect the EGR and PCV valves and clean or replace them.

Step 4: Perform a fuel pressure testing

If the P0174 error does not disappear after cleaning the mass air flow, tracing and fixing all vacuum leaks, and checking the EGR and PCV valves, check the fuel pressure. If you notice any faulty or failing fuel system components, replace them as fast as possible.

Step 5: Examine the Exhaust system

If all the above steps prove abortive or are pretty fine, then you have to narrow it down to the exhaust systems. First, examine the exhaust system and see if it is leaking. After that, inspect the oxygen sensor and the air-fuel ratio. If any of these sensors are bad, replace them. And if you find any leak in the exhaust, fix it.

Step 6: contact your mechanic

If the P0174 diagnostics trouble code is still present, there’s a likelihood you have more critical issues. Consult an experienced mechanic for a thorough diagnosis and repair. It could also mean you did not carry out a thorough diagnosis on the steps above.

How much does it cost to fix a P0174?

If you decide to have a mechanic fix the P0174 issues, you should be ready to foot the bills. Most repair shops will start with 1hr of diagnosis. And an average mechanic hourly rate is between $75 to $150.

After that, the repair shop will estimate what they’ll repair or replace to fix the P0174 error code. Depending on the culprit, you may have to pay 1 to 5 hours to fix the fault.

Here are the common parts the mechanic will likely replace at their cost.

  • Replace MAF $150 to $250
  • Clean MAF $100
  • Replace fuel pumps for $500 to $700
  • Vacuum leaks $100 to $150
  • Fuel pressure regulator $150 to $200
  • O2 sensor or air-fuel ratio sensor
  • Exhaust leak $100 to $150.


Q: How do I fix System Too Lean Bank 2?

Several issues like a bad mass air flow sensor, a lousy oxygen sensor, collapsed air filter, lousy fuel pressure regulator, bad fuel pump, and vacuum leaks from PCV hoses, intake manifold gasket, exhaust leaks. 

Once you have a P0174 error code on your car computer memory, diagnose these components, starting with minor ones like vacuum leaks, collapsed air filters, and mass air flow sensors. If those are not the culprit, narrow it down to the more expensive and unlikely probable causes.

Q: Can fuel injectors cause P0174?

One of the common causes of error code P0174 on Chevy Silverado and other car models is faulty injectors. When injectors fail to supply adequate gas to the engine for a combustion process, there will be more air than gas in that respective cylinder.

Once the engine control module (ECM) detects a compromised air-fuel mixture ratio, it’ll throw error code P0174 on the car memory. The injectors can fail because of dirty or contaminated gas.

Q: Is it okay to drive with P0174?

Driving with a P0174 error code will not cause catastrophic damages within a short period. However, if you continue driving with it for an extended period, it may cause engine overheating and even warp some internal engine components.

In any case, driving with a P0172 error code is even better than a P0174 because the P0172 means too much fuel and too little air. Too much fuel in the air-fuel mixture will keep your engine cool and prevent the engine from overheating.

Q: Can a dirty air filter cause a P0174 code?

The purpose of the air filter is to filter the air that is entering the engine. If the filter gets clogged, it’ll cause ‘engine running rich’ rather than a lean condition. However, if the engine lacks air and tries to drag air from the air intake, the pressure may cause the air filter to collapse.

When this happens, unmeasured air will mix with the air-fuel mixture and cause a lean condition.

Q: Can P0174 cause a misfire?

Yes, a lean engine will cause a misfire depending on the severity of the discrepancy in the air-fuel ratio. The misfire will be more obvious when carrying a load or when climbing uphill. Sometimes, it’ll feel like the gas pedal is unresponsive, and the car will be sluggish in movement.

Q: Can a bad O2 sensor cause a P0174 code?

The O2 sensor and the mass air flow sensor are the primary sensors that determine the amount of air-fuel mixture in the engine. If the O2 sensor fails, it’ll send inaccurate information to the engine control unit (ECU).

For instance, it can tell the car computer that there is too much oxygen in the combustion chamber. The car computer will work with this data and throw a P0174 fault code.

Final Words

The air-fuel mixture should be in the right proportion for an internal combustion process to be successful. If the ratio is compromised by more fuel or air, it will affect the overall engine performance. In any case, this will not prevent you from driving your vehicle.

But if you overlook the P0174 error code and continue driving for an extended period, you may be creating catastrophic issues in the vehicle. That’s why we explained what the P0174 fault code means, the causes, the symptoms, the diagnostics mistakes, and how to diagnose and fix the error code.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Posts