P0174: System Too Lean (Bank 2)

Did you get the P0174 code on your car scanner? Are you wondering if it’s safe to keep driving?

Keep reading for the first analysis of your situation!

  • P0174 Definition: System Too Lean (Bank 2)
  • Code type: Generic – P0174 indicates the same problem whether you’re having a Ford, BMW, or Toyota, etc.
  • Can I drive with the P0174 code? Yes, you can. However, you shouldn’t drive for too long.
  • Easy to fix? Intermediate-Expert level
  • Cost: $10-$200 (common)

Now that you have some understanding of what the P0174 code is, it will be helpful to know its symptoms and causes. Also, solutions to the various causes will be highlighted.

So, stick around!

Table Of Contents

What Does The P0174 Code Mean?

The P0174 code implies that the powertrain control module (PCM) has detected a lean condition in Bank 2. This means that there is excessive air or/and insufficient fuel in the air-fuel mixture. 

The standard air-fuel ratio: 14.7:1. 

  • 14.7 parts of air
  • 1 part of fuel

If the combustion chamber gets more than 14.7 parts air to 1 part fuel, it causes the system to run lean. 

P0174 causes, symptoms and how to fix

P0174 Causes Identification: Quick View

Usually, your scan tool throws P0174 with other codes.

This could be a bit challenging to determine the cause. So, I compiled this table to make it easier for you to diagnose the problems and fix them.

Codes CombinationCausesSolutions
P0174 + P0171 (+P0106)Loose or faulty gas cap.
Vacuum leak.
Tighten or replace the gas cap.
Smoke test & seal the vacuum leak.
P0174 + P0150 to P0167 (+ P0300)Lazy upstream oxygen sensor.Replace the oxygen sensor.
P0174 + P0100 to P0104Faulty MAF/MAP sensor.Clean or replace the MAF/MAP sensor.
P0174 + P0171 (+P0087/P0089)Stuck-open fuel pressure regulator.
Bad fuel pump.
Clogged fuel filter.
Leak fuel line.
Replace the fuel pressure regulator.
Replace the fuel pump.
Replace the fuel filter.
Replace the fuel line.
P0174 + Misfire codes (P0301 to P0312)Clogged fuel injector.Clean the fuel injector.
P0174 + P0600 to P0610Bad powertrain control module.Replace the powertrain control module.

Note: The causes for each code combination are the most common ones. There can be some uncommon issues hidden under those codes

P0174 Code Causes, Symptoms, and How To Fix

Did you find your problem? To further ensure that you actually find the right one, you need to match your car’s symptoms with the cause. 

If you don’t want to be a part changer, read on and understand your problem from the inside! 

Cause #1: Loose Or Faulty Gas Cap

Checking the gas cap is the first thing you need to do.

A loose or faulty gas cap leads to low fuel pressure, reducing the fuel injected into the combustion chamber. 

As a result, lean condition codes pop up. 

You want to ensure it is not the issue and move on to other causes.

Cause #2: Vacuum Leak

A vacuum leak will allow unmetered air into your car’s engine, leading to lean conditions on both bank 1 and bank 2.  

Therefore, the P0174 (bank 2) and P0171 (bank 1) appear at the same time, and you may also get the P0106.

Here are the symptoms of a vacuum leak:

  • P0174 activates with P0171 (sometimes with P0106)
  • Hissing sound
  • Long-term fuel trim (LTFT) > 10% (check-in “Live data” category)
  • Rough idling
  • Poor gas mileage
  • Check engine light on
  • Engine stalling

To find a vacuum leak, you should start your engine. Proceed to spray water on the vacuum hoses; if there is a leak, the water will get sucked into the hose.  

In some cases, you have to do a smoke test.

The most common causes of vacuum leaks are a cracked hose or a loosened clamp. To fix this problem, replace the hose or tighten the clamps.

Watch this video to know how to find and fix vacuum leaks.

Cause #3: Lazy Upstream Oxygen Sensor

The upstream O2 sensor (located before the catalytic converter) helps the PCM adjust the air-fuel mixture. This is done by measuring the amount of O2 in the exhaust gas. 

If your car has a lazy oxygen sensor (bank 2 sensor 1), it can underreport the amount of oxygen. 

This data tells the PCM to send too little fuel compared to the amount of air coming into the engine, causing the lean condition. 

The charts below represent the O2 sensor (good and bad) output voltage.

When the O2 sensor voltage reaches 0.6v, the PCM reduces the fuel. Otherwise, when the value drops below 0.3v, the PCM raises the fuel. The red line should fluctuate in this range continuously.
This is a typical voltage chart of a “lazy” O2 sensor. The amplitude is smaller and the red line fluctuates above 0.45v. This data tells the computer to reduce the fuel.

You can diagnose a lazy upstream oxygen sensor by looking out for the following symptoms:

  • P0174 and P0150 to P0167 are triggered (occasionally with P0300)
  • Bad gas mileage
  • Check engine light on

In the event of a lazy upstream oxygen sensor, you should completely replace the oxygen sensor. Replacing the oxygen sensor is a simple, inexpensive procedure so you can do it by yourself.

Try to replace the oxygen sensor with this video.

Cause #4: Faulty MAF/MAP Sensor

The data of the Mass Air Flow (MAF)/ Manifold Absolute Pressure (MAP) sensor is used to calculate the amount of intake air and adjust the fuel injected into the combustion chamber. 

If the MAF/MAP sensor malfunctions, it will transfer inaccurate data to your car’s computer, and the air-fuel ratio will be compromised. 

Then, this leads to a lean condition, which causes the combination of P0174 and P0100 to P0104 to appear on your scan tool.

The symptoms of a faulty MAF/MAP sensor include:

  • P0174 and P0100 to P0104 error codes activate
  • Hard starting
  • Check engine light on 
  • Misfiring 
  • Rough idling
  • Engine stalling
  • Bad fuel economy

The best way to combat this problem is to clean or replace the MAF/MAP sensor. You can do it yourself as it isn’t too complex. 

Here’s how you can do it.

Cause #5: Low Fuel Pressure

Low fuel pressure in your fuel system will lead to less fuel in the combustion chamber. It causes a lean condition in both bank 1 and 2, causing the P0174 and P0171 at the same time. 

Several factors can lead to low fuel pressure. 

  • Stuck-open fuel pressure regulator (FPR)
  • Bad fuel pump
  • Clogged fuel filter
  • Leak fuel line

Symptoms of low fuel pressure are:

  • P0174 and P0171 are activated (sometimes P0087/P0089) 
  • Hard starting
  • Whining noise 
  • Engine stalling
  • Misfires
  • Check engine light on
  • Fuel smell (leaking fuel line)

To fix this problem, find the cause and replace the faulty component. This is not easy to find the cause and the cost to replace some of the components can be expensive.

Cause #6: Clogged Fuel Injector

Clogged fuel injectors (in cylinders 2, 4, 6, 8, etc.) will be problematic to your engine as they will not supply enough fuel into the combustion chamber. 

Consequently, this results in your engine leaning in Bank 2. By implication, the P0174 will activate with misfire codes (P0301 to P0312) on your scan tool. 

The symptoms of a clogged fuel injector include:

  • P0174 and misfire codes (P0301 to P0312) appear 
  • Misfiring
  • Check engine light on
  • Rough idling
  • Engine stalling
  • Bad fuel economy 

If your engine is lean due to a clogged fuel injector, clean the fuel injector thoroughly. 

Here’s how you can clean it.

Cause #7: Bad Powertrain Control Module

The PCM tries to maintain the standard 14.7:1 air-fuel ratio by pumping fuel into the mixture. In case you have a bad PCM, it may supply too little fuel when regulating the air-fuel ratio. If this happens, P0174 is triggered with P0600 to P0610. 

You will need to replace the PCM to get rid of this problem.

However, this is a rare situation and should be your last conclusion.

Also, replacing the PCM is a complicated process. Find a skilled mechanic to do it for you. 

How Much Does It Cost To Fix The Code P0174?

Based on the cause, resolving the P0174 code will usually cost as low as $10 or up to $200.

If a faulty gas cap is a problem (this happens regularly), you can easily fix it at $10-$20.

Depending on the severity, you’ll spend $10-$200 fixing a vacuum leak. If you fix it by yourself, you will spend just a few dollars. However, if there’s a leak in a critical area, it gets more expensive.

If the cause of the P0174 code is a faulty oxygen sensor, you should replace it, costing $20-$130.

The estimated repair cost of P0174

SolutionsEstimated Cost
Replace the gas capDIY: $10 - $20
Repair shop: $25 - $40
Fix the vacuum leakDIY: $10 – $200
Repair shop: $150 – $1,000
Replace the oxygen sensorDIY: $20 - $130
Repair shop: $70 - $250
Clean the MAF/MAP sensorDIY: $15
Repair shop: $50 - $100
Replace the MAF/MAP sensorDIY: $30 - $300
Repair shop: $80 - $380
Replace the fuel pressure regulatorDIY: $50 - $200
Repair shop: $150 - $350
Replace the fuel pumpDIY: $95 - $850
Repair shop: $220 - $1,100
Replace the fuel filterDIY: $10 - $70
Repair shop: $50 - $175
Replace the fuel lineDIY: $10 - $150
Repair shop: $200 - $500
Clean the fuel injectorDIY: $10
Repair shop: $60 to $100
Replace the PCMDIY: not recommend
Repair shop: $1,000 - $3,000

Note: The data in this table is collected in June 2022. The price depends on many factors, such as your car’s make and year, mechanic’s fee, etc. 

You Ask, I Answer

Getting the P0174 code on your scan tool is not a call for panic. Instead, it is meant to draw your attention to a specific engine fault causing the malfunction. Fortunately, you now know the various causes of the P0174 code, their symptoms, and how to fix them.

So, what are your thoughts? Can you think of other causes of the P0174 Code? If you can, let us know in the comment section. 

Also, if you have any questions, leave a message, and I will ensure to get back to you ASAP!

See ya!

Read more: The 9 Best OBD2 Scanners for 2022: The Only Review You Need

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