If there is too much air and not enough fuel in the air-fuel ratio (AFR), a lean state will be produced. The engine Control Module will detect the lean condition and generate a check engine code P0174. The ECM is built to be able to make modest to moderate adjustments to return a lean condition to normal. This code may also appear if the air-fuel ratio needs more adjustment to get back to normal than the ECU is able to provide.
Let’s dive into the details.
What is Code P0174?
The diagnostic trouble code P0174 refers to a problem with the fuel system in a vehicle’s engine, explicitly indicating that the fuel mixture is too lean (i.e., there is too much air relative to the amount of fuel) in bank 2 of the engine.
This code is available in vehicles with a V6 or V8 engine with two banks of cylinders, such as some models from Ford, GM, and Toyota. A lean fuel mixture can cause various drivability issues, including rough idle, misfires, reduced engine power, and increased emissions.
What are the Causes of the P0174 Code?
The P0174 diagnostic trouble code indicates that the engine is running too lean (i.e., too much air and not enough fuel) in bank 2 of the machine. The following are some possible causes of a P0174 code:
A vacuum leak in the engine’s intake system can allow unmeasured air to enter the engine, disrupting the air-fuel mixture and causing the engine to run lean.
Faulty Mass Air Flow (MAF) sensor:
The MAF sensor measures the air entering the engine and sends this information to the engine control module (ECM). A faulty MAF sensor can cause incorrect readings, producing a lean air-fuel mixture.
Malfunctioning oxygen (O2) sensor:
The O2 sensors in the exhaust system measure the amount of oxygen in the exhaust gas and send this information to the ECM to adjust the air-fuel ratio. A faulty O2 sensor can cause the ECM to add too much air, resulting in a lean air-fuel mixture.
Clogged fuel filter or fuel injectors:
A clogged fuel filter or fuel injector can restrict fuel flow to the engine, resulting in a lean air-fuel mixture.
Malfunctioning fuel pressure regulator:
The fuel pressure regulator controls the amount of fuel that to the engine. A faulty fuel pressure regulator can cause too little power to be sent to the engine, resulting in a lean air-fuel mixture.
An exhaust leak between the O2 sensor and the engine can allow excess air to enter the exhaust system, resulting in a false lean reading and triggering the P0174 code.
Malfunctioning PCV valve:
The positive crankcase ventilation (PCV) valve regulates the amount of air that enters the engine’s crankcase. However, a faulty PCV valve can allow too much air into the machine, which results in a lean air-fuel mixture.
What are the Symptoms of a P0174 Code?
When a vehicle’s engine generates a P0174 code, the air/fuel mixture in bank 2 of the machine is too lean. It leads to a variety of symptoms, which can include:
Check Engine Light (CEL) illumination:
The most common symptom of a P0174 code is the illumination of the CEL on the vehicle’s dashboard. The CEL can indicate a variety of issues, including a P0174 code.
A lean air/fuel mixture can cause the engine to run wild or shake while idling.
A lean air/fuel mixture can cause a vehicle to have reduced power or acceleration, especially when going uphill or accelerating from a stop.
A lean air/fuel mixture can cause cylinders to misfire, leading to rough engine performance, backfiring, and poor fuel economy.
Increased fuel consumption:
When the engine is running lean, it may require more fuel to operate correctly, however, which can cause an increase in fuel consumption.
Hesitation or stumbling during acceleration:
A lean air/fuel mixture can cause uncertainty or stumble during acceleration, especially when the engine is under load.
How to Fix the P0174 Code?
Fixing a P0174 code typically involves diagnosing the underlying issue causing the lean air/fuel mixture in bank 2 of the engine. Here are some common steps that a mechanic may take to fix a P0174 code:
Check for vacuum leaks:
A leak can allow unmeasured air to enter the engine, causing a lean air/fuel mixture. A mechanic may use a smoke machine or a vacuum gauge to locate and repair any vacuum leaks in the engine’s intake system.
Replace the Mass Air Flow (MAF) sensor:
A faulty MAF sensor can cause a lean air/fuel mixture. A mechanic may test the MAF sensor using a scan tool or a multimeter and replace it if it is faulty.
Replace the oxygen (O2) sensor:
A malfunctioning O2 sensor can cause the engine to run lean. A mechanic may test the O2 sensor using a scan tool and replace it if it is faulty.
Check fuel pressure and replace fuel filters or fuel injectors:
A clogged fuel filter or fuel injector can restrict fuel flow to the engine, causing a lean air/fuel mixture. A mechanic may check fuel pressure and replace the fuel filter or fuel injectors.
Check the fuel pressure regulator:
However, a faulty one can cause too little fuel to be sent to the engine, causing a lean air/fuel mixture. A mechanic may test the fuel pressure regulator and replace it if it is faulty.
Repair exhaust leaks:
An exhaust leak can cause false readings from the O2 sensor, leading to a lean air/fuel mixture. A mechanic may locate and repair any exhaust leaks between the O2 sensor and the engine.
Replace the Positive Crankcase Ventilation (PCV) valve:
A faulty PCV valve can cause too much air to enter the engine, leading to a lean air/fuel mixture. A mechanic may test the PCV valve and replace it if it is faulty.
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How Much Does it Cost to Fix Code P0174?
The cost to fix a P0174 code can vary depending on the underlying issue. Here are some factors that can impact the cost of repairs:
Diagnosing the underlying issue causing the P0174 code can take time and labor, which can vary depending on the make and model of the vehicle. Diagnostic fees can range from $50 to $150 or more.
The cost of parts can vary depending on what needs to replacement to fix the issue causing the P0174 code. For example, replacing a faulty MAF sensor can cost between $100 and $300, while returning a fuel filter costs around $50.
The cost of delivery can vary depending on the complexity of the repair and the hourly rate of the mechanic. Labor costs can range from $100 to $200 per hour.
However, the cost to fix a P0174 code can range from a few hundred dollars to over $1,000 or more, depending on the specific issue and the make and model of the vehicle. It is essential to have a qualified mechanic diagnose and repair the problem to ensure that the repair is correct and to prevent further damage to the engine.
P0174 Code – FAQs
A P0174 code means that the air/fuel mixture in bank 2 of the engine is too lean, indicating that there is too much air or insufficient fuel in the mix.
A variety of issues, including vacuum leaks, a faulty MAF sensor, a faulty oxygen sensor, a clogged fuel filter, a faulty fuel pressure regulator, and more, can cause a P0174 code.
Symptoms of a P0174 code can include a check engine light, rough idle, poor acceleration, misfires, increased fuel consumption, hesitation or stumbling during acceleration, and more.
A mechanic can diagnose a P0174 code using a scan tool to read the code and access the vehicle’s computer. They may also visually inspect the engine components and use diagnostic equipment to check for vacuum leaks, test the MAF sensor and oxygen sensor, and more.
It is not good to drive a vehicle with a P0174 code for an extended period, as running a car with a lean air/fuel mixture can cause more severe engine problems over time. It is best to diagnose and repair the issue with a qualified mechanic as soon as possible.
Fixing a P0174 code typically involves diagnosing the underlying issue causing the lean air/fuel mixture and repairing or replacing the faulty component, such as a vacuum leak, MAF sensor, oxygen sensor, fuel filter, or fuel pressure regulator. The cost of repairs can vary depending on the specific issue and the make and model of the vehicle.