P0174 Code: Causes, Symptoms and How to Fix it

The P0174 code is a common diagnostic trouble code (DTC) that indicates a problem with your vehicle's air-fuel mixture. Specifically, this code refers to a thin fuel condition in the engine and indicates that the Engine Control Module (ECM) has detected a high air-fuel ratio (too much air, not enough fuel) in cylinder #2. While a single lean condition may not cause immediate serious damage, ignoring the problem can lead to poor engine performance, increased emissions and even long-term damage.

In this article, we'll take an in-depth look at the cause of the P0174 code, the symptoms that may alert you to the problem, and most importantly, how to fix it effectively using a diagnostic scanner and proper repair methods. Understanding and resolving P0174 codes promptly will help ensure that your engine runs smoothly and efficiently, keeping your vehicle in tip-top shape.

Meaning of P0174 Fault Code

The system is too lean (Lean Condition): This means that the engine has more air in the combustion chamber of Bank 2, or the fuel supply is insufficient, resulting in a less-than-ideal combustion mixture.

Bank 2: Most engines have two-cylinder banks called “Bank 1” and “Bank 2”. In a V-type engine, “Bank 1” is usually the side near the engine timing chain or belt, while “Bank 2” is the opposite side.

Common Causes of P0174 Error Codes

Air filter or intake system leaks:

Leaks in the intake piping, air filter, or related seals can cause outside air to enter the engine and affect the air-to-fuel mixing ratio.

Fuel injection system failure:

Clogged or malfunctioning injectors may result in an inadequate fuel supply, causing a lean mix ratio.

Oxygen sensor failure:

A faulty oxygen sensor in Bank 2 may cause the engine control module to fail to accurately detect the air-fuel ratio, triggering the P0174 error.

Low fuel pressure:

Insufficient fuel pump pressure, or a clogged fuel filter, may result in an erratic fuel supply, affecting normal engine operation.

Mass airflow sensor (MAF) malfunction:

A mass air flow sensor that does not detect the correct airflow may cause the engine control module to misjudge the air-to-fuel mix ratio.

Air Leak Problems (Vacuum Leaks):

If a vacuum line is cracked or loose, air can enter the engine and not be accounted for, resulting in a lean air-fuel ratio.

ECM (Engine Control Module) Failure:

In some cases, a malfunction in the engine control module can also cause the wrong fault code to appear.

P0174 Symptoms of Error Codes

Erratic engine idle: a lean mixture ratio may cause the engine to idle erratically, and the owner may notice fluctuations in engine speed.

Weak acceleration: the engine may exhibit a lack of power during acceleration due to insufficient fuel supply.

Increased Fuel Consumption: Too much air and not enough fuel can lead to reduced engine efficiency, which in turn increases fuel consumption.

Engine judder or knocking: Lean mixture ratios may lead to incomplete combustion, resulting in engine judder or knocking.

Increased emissions: An incomplete combustion process due to too much air may lead to increased exhaust emissions and may even trigger fault codes in the emission system.

How to Fix P0174 Code with the XTOOL Diagnostic Tool

1. Connect the XTOOL Diagnostic Tool

• Prepare the Tools: Ensure that you have an XTOOL diagnostic tool that supports P0174 code diagnostics and repair (e.g., XTOOL IP919, XTOOL D Series).
• Connect the Diagnostic Tool: Plug the XTOOL diagnostic tool into the OBD2 port of your vehicle. This port is typically located under the driver's side dashboard.

XTOOL D9S

XTOOL IP919 PRO

2. Start the Diagnostic Tool and Read the Codes

• Turn on the Ignition: Start the vehicle to ensure the diagnostic tool can communicate with the vehicle's ECU.
• Run XTOOL Diagnostic Software: Open the XTOOL device and enter the "Diagnostics" mode. Select your vehicle make and model, then begin the scan.
• Read the P0174 Code: After scanning, the diagnostic tool will display all fault codes. Confirm the presence of the P0174 code. The tool will also show you the detailed fault description and possible causes.

3. Inspect and Clear the Fault Code

• Review Fault Code Information: The XTOOL diagnostic tool will display the P0174 description, which may indicate issues such as air intake problems, fuel supply issues, or vacuum leaks.
• Clear the Fault Code: After identifying and fixing the problem, use the XTOOL diagnostic tool to clear the fault code. Click the "Clear Codes" button to reset the vehicle's system and verify if the repair was successful.

4. Check and Fix Common Causes of the P0174 Code

When using the XTOOL diagnostic tool to fix the P0174 code, here are some common causes and corresponding repair methods:

a) Air Filter or Intake System Leaks

• Steps:
• Use the XTOOL diagnostic tool to view engine intake system data, such as MAF flow, air pressure, etc.
• Inspect the intake pipes, air filter, and seals for cracks or looseness.
• Monitor related data using the diagnostic tool to verify if there are any abnormalities.
• Fix: Replace or repair damaged air filters and intake seals.

b) Fuel Injector Issues (Clogged or Malfunctioning)

• Steps:
• Use the XTOOL diagnostic tool to read injector data and check if the fuel flow is normal.
• Inspect the fuel injectors for any clogs or damage.
• Fix: Clean or replace faulty injectors. XTOOL can also perform injector activation tests to ensure they are working properly.

c) Oxygen Sensor Issues

• Steps:
• Use the XTOOL diagnostic tool to view oxygen sensor data and check if the sensor on Bank 2 is functioning correctly.
• If the oxygen sensor shows irregular readings (e.g., voltage fluctuations), it may need to be replaced.
• Fix: Replace the faulty oxygen sensor.

d) Low Fuel Pressure

• Steps:
• Use the XTOOL diagnostic tool to monitor fuel system pressure data.
• Check if the fuel pump and fuel filter are working properly to ensure consistent fuel pressure.
• Fix: If fuel pressure is abnormal, check and replace the fuel pump or clean/replace the fuel filter.

e) MAF Sensor Malfunction

• Steps:
• Use the XTOOL diagnostic tool to read data from the MAF sensor and ensure accurate airflow readings.
• Check for dirt or damage to the MAF sensor.
• Fix: Clean or replace the MAF sensor if necessary.

f) Vacuum Leaks

• Steps:
• Inspect all vacuum lines and fittings, especially those related to the ECM and air intake system.
• Use the XTOOL real-time data stream function to check intake pressure and air-fuel mixture.
• Fix: Repair any loose or damaged vacuum hoses and connections.

5. Perform Field Testing with XTOOL

After completing the repairs, perform field testing using the XTOOL diagnostic tool to ensure the fix is successful:

• Real-time Data Monitoring: Monitor key data such as airflow, fuel pressure, and oxygen sensor signals using the XTOOL tool to confirm the system has returned to normal.
• Road Test: Perform a short road test to observe the vehicle’s driving performance, including acceleration, idle, and emissions.

6. Clear the Fault Code and Confirm Repair

Once all repairs are completed and verified through testing, use the XTOOL diagnostic tool to clear the fault codes. This resets the vehicle's system and ensures that the P0174 code does not reappear.

Fixing the P0174 code with an XTOOL diagnostic tool is a systematic process. By reading the fault code, monitoring real-time data streams, and checking common fault sources, you can quickly pinpoint and fix the issue.