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Ford Taurus 3.0L Duratec Engine P0171 and P0174 Codes: Diagnosis Tips and Normal Sensor Data Values

Model: Ford Taurus Fault Code: P0171 Posted: 2009-01-01 10:55

Hi, I'm currently troubleshooting a 1998 Ford Taurus with a 3.0L Duratec engine that is displaying OBD2 fault codes P0171 and P0174. I've already cleaned both the Mass Air Flow (MAF) sensor and EGR valve, but the codes persist. The vehicle runs smoothly under normal conditions, which makes this issue particularly puzzling. I'm using a diagnostic tool that provides extensive engine data—up to 8 pages of readings including MAF flow volume, intake pressure, and fuel trim values. However, I can't find any official or reliable source listing the 'normal' operating ranges for these parameters on a Duratec engine. While many users share individual value examples online, there's no comprehensive reference list available. My question is: Is there an authoritative list of normal sensor readings (such as short-term and long-term fuel trims) that I can compare against my current data to identify deviations? Any guidance or resources would be greatly appreciated. Thanks in advance for your help!

Related fault codes
P0171P0174
Comments (3)
Anonymous 2009-01-01 20:08

Vacuum leaks—especially in the PCV system—are a common cause of P0171 and P0174. These can be hard to detect due to limited access, but check thoroughly. Monitor the short-term fuel trim values; if they are significantly elevated (typically above +4%), this indicates a leak. The engine control module will trigger these codes when fuel trims reach around +18% or higher.

Anonymous 2009-01-02 19:36

Common causes include induction air leaks, vacuum leaks, weak fuel pump, restricted fuel filter, or exhaust leaks near the upstream oxygen sensor. A professional diagnostic using smoke testing is often effective for locating such leaks. If possible, please share your freeze frame data (especially the Long Term Fuel Trim % value). This helps pinpoint whether the issue stems from a lean condition or fuel delivery problem.

Anonymous 2009-08-02 13:02

I have a 2000 Ford Taurus that had the codes P0171 & P0174, after reading these posts I checked the vacumm lines and found that the elbow on the PCV valve was split. I replaced it and the valve (total cost $3.98) and it is running fine.