P0174 engine code in Ford, Chevy, BMW: Causes, Fixes

The P0174 is a diagnostic trouble code indicating the system is too lean, which initiates when the air-fuel ratio in your vehicle is too lean. The gas must first combine with oxygen before combustion and powering your vehicle. Several vehicle manufacturers recognize, such as Toyota, BMW, Nissan, and Dodge. You will likely experience issues with your car if the mixture is too lean.

The error codes that will show up during a lean situation are P0174 and P0171. The latter triggers when the condition happens in cylinder bank 1, while the former is in cylinder bank 2. The engine control module (ECM) can provide a limited restoration of your vehicle to a normal state during a lean situation. It throws the P0174 code if it cannot restore it, so a user can intervene and fix the issue.

The following sections thoroughly discuss everything you should know about these error codes. 

2007 BMW series 3 328i

What does code P0174, “system too lean (bank 2),” mean?

The error message means the same whether you have a Chevy Silverado, a Ford F150, or a Toyota Highlander. It indicates that the Engine Control Module (ECM) detected a lean condition, which means insufficient fuel and too much air in the engine.

The Engine Control Module (ECM) can adjust the lean condition to its normal state. However, its capabilities are limited, so it will not always address the issue. The P0174 code triggers if it requires more compensation to return to normal levels.

What causes the P0174 code?

Are you wondering about the common causes of this error? The following are the common culprits to it. After going through this list, it is possible you will not find the one causing the error.

  • Blockage in the fuel filter and fuel injectors – Blockage in either of these parts results in an imbalance in the fuel and air ratio. Bad or clogged fuel injectors will result in a bad fuel pump, causing several other issues. The only way to address this issue is by removing the injectors from the engine. You can send the injector to a professional cleaning service provider for proper handling and cleaning. These service providers typically use a cleaning solution to resolve the issue. Depending on the severity of the clog, they may use other substances. You can clean it yourself if you know how.
  • Defective oxygen sensor – A defective oxygen sensor may incorrectly provide the oxygen levels in the engine, resulting in inaccuracies. Before combustion occurs in your vehicle, it needs to combine with oxygen first. It may not provide the correct level if the oxygen sensor is defective.
  • Faulty mass airflow (MAF) sensor – A defective or faulty mass airflow sensor will cause extreme lean conditions because it underestimates the air flowing through the engine. A defective MAF sensor can usually be mistaken for a faulty fuel pump assembly.
  • Issues with PCM – The powertrain control module (PCM) is a control unit component of an engine. It is usually a combination of the transmission control unit (TCU) and engine control unit (ECU). The PCM controls over 100 factors in your vehicle. It manages your transmission, engine, and other parts, so it receives the correct information from one to another.
  • Leakage in the brake booster – Brake fluid is the number one root cause of leakage in the brake booster. It causes the rubber diaphragm to fail, triggering the P0174 code.
  • The fuel pump is getting weak – A weak fuel pump is an issue because there is a lack of pressure. It will cause your vehicle to crank. More severe cases will require you to crank the engine several times before it starts.
  • The vacuum connector or PCV line may have cracks or damage – The PCV or vacuum connector is an important part of the engine because it regulates the pressure. It allows the spark, fuel, and air to work together.
  • Weakening fuel pressure regulator – A weakening fuel pressure regulator will cause a drop in fuel efficiency, misfires, acceleration reduction, and power reduction. Other causes may also trigger these issues, so we recommend getting a diagnosis from a trusted service center. You may encounter the P0300 error because of multiple misfires.

Cost of diagnosing the P0174 code

The diagnostics cost depends on a few things, including location and service center labor rates. Diagnostic cost range between USD 70 to USD 150. It does not include the cost of fixing the problems or issues, which we will cover in the next section.

2007 BMW series 3 328i from the back

Several factors can cause a P0174 error, which explains the varying associated costs. The diagnostic cost is not the cost to repair or fix the issue. It is usually a separate fee automotive shops charge. The following section lists the top procedures for these issues, including their estimated fee. 

How much does it cost to fix P0174?

The following are the cost of the top fixes most people need. Fuel pump cleaning or replacement is the most expensive, costing between USD 1,300 to USD 1,700. Vacuum leaks take second place, costing about USD 1,000. Cleaning the MAF sensor is the cheapest, roughly costing only USD 100.

We recommend scanning through the table below for an estimate of how much you need to spend to fix the error code. 

ItemEstimated cost
Cleaning MAF$100
Defective O2 sensor$325-400
Exhaust gas leak$300-400
Fuel pressure regulator$200-400
Fuel pump$1300-1700
Oxygen sensor or air-fuel sensor$200-300
Repairing exhaust$100-200
Replacing MAF$300
Replacing PCV valve$75-100
Replacing spark plug$150
Vacuum leaks$1,000

What are the symptoms of the P0174 code?

Several symptoms manifest. However, we will not cover everything. The following symptoms below are the most common ones vehicle owners experience.

  • Your vehicle dashboard has a “Check Engine Light” indicator. There is an issue if it lights up.
  • Accelerating your vehicle requires more engine power. Your engine is not performing at its best if there is inadequate power.
  • Your vehicle’s idling is rough.
  • The engine is stalling.
  • You will notice an increase in the fuel consumption of your vehicle.
  • Your engine begins to misfire.

Lean vehicles emit nitrogen oxide (NOx), which is detrimental to your health. It causes problems in your respiratory system, such as asthma. It can also lead to misfires, damage to the internal components, and cause problems with the catalytic converter. We highly recommend that you take your vehicle to the nearest store specialist if you experience any of the issues above.

How does a mechanic diagnose the P0174 code?

Chevy

A mechanic will usually take the following steps when diagnosing the P0174. Some may have a slightly different approach, and that is fine. However, the steps below are the most basic ones that should always be part of the process.

  1. The mechanic performs a fuel pressure test.
  2. It checks the vacuum lines and intake system for leaks.
  3. Check the valve cover for leaks or worn hoses.
  4. Inspect the Positive Crankcase Ventilation (PCV) valve.
  5. Test the mass air flow sensor using a multimeter or a scan tool.
  6. Test the oxygen sensors using a multimeter or a scan tool.

Common mistakes when diagnosing the P0174 code?

The two most common diagnosing mistakes are the following:

  • Replacing or deeming a component is malfunctioning without testing.
  • Failing to check for leaks and tears in the intake system.

Please refer to the below information for the DIY steps for conducting a diagnostic test. Having a good understanding of automotive is a valued skill. You must be at least an intermediate-level driver, so we recommend against it for beginners.

Pliers, screwdrivers, mass airflow cleaners, the vehicle’s instruction manual, and fuel pressure testing gauges are some tools/parts you need for your DIY project.

  1. Scan your entire vehicle, ensuring no other code is present.
  2. Look into the vacuum lines and look for leaks. A proper and sealed connection is appreciated.
  3. Check the mass airflow (MAF) sensor.
  4. Inspect the fuel pressure.
  5. Inspect the vehicle’s exhaust system.

How serious is the P0174 code?

The P0174 error code does not always require immediate action. It will not damage your car right away. However, driving with a lean engine may lead to internal engine parts failure and overheating issues. We recommend getting it fixed right away.

Most mechanics recommend running rich is the preference than running slow. Some drivers will ignore the error because they do not notice anything wrong with the vehicle. Avoid full acceleration pulls if you see this error code. We recommend driving slowly to the nearest service center to have the issue inspected.

How do I fix code P0174?

Fixing the P0174 depends on the cause of the error. We recommend taking it to the closest automotive store or service center for proper diagnostics. The fix will vary depending on the root cause.

The following are the possible fixes for this error:

  • Replace or clean the mass airflow sensor
  • Replace the oxygen sensor
  • Replace the vacuum lines
  • Replace the EGR and PCV valve
  • Replace the brake booster and valve cover gasket
2010 Ford f-150 FX4 Pickup 4D

Troubleshooting code P0174

You can troubleshoot the P0174 by analyzing the causes of the error code. Knowing the cause will help you narrow down the troubleshooting steps. We suggest referring to the previous sections of this article for more details.

OBD-II Scan Codes

All vehicles have an onboard diagnostics (OBD) system. The first vehicles to have it were manufactured in 1996 when automakers implemented a universal system for it. A central computer system is the core of the onboard diagnostics. There is a network of sensors across the vehicle, with connection points for each. The onboard diagnostics system gives an overview of everything that is working and not working. It provides near real-time alerts/warnings.

The OBD-II system records any engine operating conditions that go at fault. We call the data gathered freeze frame data because it represents a single information frame stored in the system memory.

Higher priority codes, such as ones affecting the engine or the catalytic converter, will overwrite an original freeze frame data. Low catalyst system efficiency will prompt a P0420 code.

What do OBD diagnostics signify?

An array of sensors produce the OBD-II codes that relate to vehicle functionality. The connectors rest on a steering column. Mechanics can access these through a port.

The ECM is the system’s brain, collecting all the information from the sensors to optimize its performance. It also performs several self-checks to clear anything in storage.

What is DTC?

The diagnostic trouble codes (DTC) send information to the ECU if it falls beyond the normal range. The DTC is an array of letters and numbers responsible for locating the nature and source of the issue. The OBD-II refers to the entirety of the DTC system, including:

  • network
  • body
  • powertrain
  • and chassis codes.

An indicator light is a medium where the ECU sends information. The issue relates to safety-related faults and emissions systems if the check engine light or malfunction indicator light (MIIL) is on. A flashing MIIL indicates a more severe issue underhand, causing damage to critical parts of the system. These may include air induction, internal engine fuel, or catalytic converter.

2010 Ford f-150 King Ranch

How are OBD-II codes utilized?

The OBD-II alerts you of any issues with your car. You will usually find the access port under the steering column. A mechanic will access the port using an OBD-II scanner. They use the results as a base point for any diagnostic work. You will find the standard five-digit code across several models and makers. However, some manufacturers use OEM codes for specific vehicles. You will need higher-quality scanners to access these. 

What are the OBD Codes Types?

There are four types available. These are as follows:

  • P – Engine and transmission systems
  • B – Body
  • C – Chassis
  • U – Wiring and network systems

FAQ

The following are the frequently asked questions.

Can an exhaust leak cause a P0174 code?

The ECU detects a false lean signal when an exhaust leak is happening. As a result, it responds incorrectly. 

Is it OK to drive with the P0174 code?

Driving with this error code does not immediately damage your vehicle. However, leaving it unattended for an extended period will cause damage. Your engine may overheat, damaging the internal parts.

It is tempting for most people to ignore the warning sign because there are no noticeable problems with their vehicle. 

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