The most efficient combustion engines use an air-fuel ratio of 14.7 parts air to 1 part fuel. A lean condition occurs when there is more than 14.7 parts of air for every 1 part of fuel, which triggers the P0174 code.
A lean state can be caused by a vacuum leak that allows too much air into the mix, or a fuel system that doesn’t supply enough fuel. The powertrain control module (PCM) tries to fix the lean condition by adding more fuel to keep the mixture at the correct 14.7:1 ratio. A code P0174 appears when these adjustments become too large.
The diagnostic trouble code (DTC) P0174 shows ‘System Too Lean (Bank 2).’ This means the air-fuel mixture in your vehicle is too lean. For your car to run, the fuel needs to mix with oxygen before it burns.
The mixture burns completely when the air and gas are present in the correct proportions. Your vehicle will not run efficiently if the mixture is too lean.
The codes P0171 and P0174 appear when the engine is in a lean condition. The P0171 code activates when cylinder bank 1 is in a lean condition, while the P0174 code activates when cylinder bank 2 is in a lean condition.
The Engine/Powertrain Control Module (ECM/PCM) can fix a lean situation to some extent. However, it stores the P0174 code to alert you to resolve this issue.
P0174 code causes
The P0174 engine code indicates that there is an issue with the air/fuel ratio provided to your engine. There are several reasons for this, ranging from air leaks and fuel injector issues to malfunctioning sensors. These include:
- Faulty mass airflow (MAF) sensor
- Presence of blockage in the fuel filter and fuel injectors
- The fuel pump is getting weak
- Weakening the fuel pressure regulator
- The vacuum connector or PCV line can have cracks or damage
- Defective oxygen sensor
- Issues with PCM
- Leakage in the brake booster
Symptoms of the P0174 code
You may notice the following symptoms if your vehicle has an error code P0174.
- Check Engine Light turns on
- Decrease in engine performance. You will feel a lack of power while accelerating.
- The engine starts to misfire
- Increase in fuel consumption
- Rough idling
- Engine stalling
Lean-running vehicles release nitrogen oxides (NOx), which can harm your health and lead to respiratory issues like asthma. Running your engine lean can also cause misfires. These misfires can damage your car’s catalytic converter and other parts over time. If you notice any of these symptoms, take your car to a qualified technician as soon as possible.
