The ideal air/fuel ratio is 14.7:1 (14.7 parts air to one part fuel). P0174 is a generic code, so it has the same meaning for the Mazda 6 as any other vehicle.m Here’s all three parts of the definition, divided by its three parts: Fuel Trim System P0174 Definition: Fuel Trim System – Lean (Bank 2) The common P0174 repairs are usually simple. It varies, but the most common repairs are usually under $200. The most common causes of P0174 are a vacuum leak or a dirty MAF sensor.Ĭheck engine light, decreased fuel economy, misfire, hard to find idle.ĭirty MAF sensor, vacuum leak, O2 sensor. If they appear together, it reduces the list of potential causes (more on that in the last section of the article. P0174 and P0171 (fuel trim lean bank one) are the most frequently seen air/fuel mixture-related codes. It indicates that your Mazda 6 is running lean on the bank two side of the engine. One of the most common trouble codes with the Mazda 6 is P0174.