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2006 Ford Taurus P0174, P0420, P0171, P0316 Diagnosis and Repair Guide

Model: 2006 Ford Taurus Fault Code: P0171 Posted: 2021-02-15 12:01

My girlfriend's daughter drives a 2006 Ford Taurus with 86,000 miles. The vehicle is currently displaying active OBD2 diagnostic codes: P0174 (Rich mixture on bank 2), P0420 (Catalyst Efficiency Below Threshold), P0171 (Lean mixture on bank 1), and P0316 (Misfire upon startup). Based on research, my planned troubleshooting steps include: 1) Clean the Mass Air Flow (MAF) sensor 2) Inspect for vacuum leaks 3) Replace the air filter 4) Replace spark plugs 5) Replace ignition wires 6) Any additional recommendations? I'm currently using a Bluetooth OBD2 scanner connected to my phone via Torque Pro. While it allows me to clear codes and view basic fault information, I'm unsure if it provides fuel trims or real-time data streams that are commonly recommended for diagnosing these issues. I'm seeking advice on the most effective diagnostic approach and whether a more advanced scan tool is necessary.

Related fault codes

P0171P0174P0316P0420

Comments (6)

Anonymous 2021-02-16 08:12

Check Stoichiometric Fuel Trims (Stft and Ltft) under various load conditions. P0316 indicates a misfire at startup—this could have caused damage to the catalytic converter, especially if sustained. Lean codes on both banks suggest possible vacuum leaks or dirty MAF sensor. A vacuum leak affecting both cylinders is likely. Low fuel pressure should also be ruled out. If trims improve under load, it may point to a vacuum leak; if they worsen, consider a dirty or restricted MAF sensor or low fuel pressure. Monitor the oxygen sensor voltage while driving at wide-open throttle (WOT)—it should remain high when the pedal is fully depressed. A drop in voltage could indicate fuel delivery issues. Also consider clogged or dirty fuel injectors. These are just some thoughts—let me know if I can assist further.

Anonymous 2021-02-16 08:24

Focus on fuel trims, MAF sensor cleanliness, vacuum leaks, and low fuel pressure. It's possible the catalytic converter has been damaged due to prolonged misfiring. Clear all codes and monitor if they return. If fuel trims improve under load, perform a vacuum leak test: use a water bottle with a hole in the cap, apply it to suspected gaskets, EGR valves, or hoses, and listen for suction sounds. Any audible intake of water indicates a vacuum leak.

Anonymous 2021-02-16 09:40

Thanks, autojoe. I think I'll need to invest in a more reliable scan tool to get accurate data streams and fuel trim readings.

Anonymous 2021-02-16 11:27

Does your scan tool support real-time data stream monitoring? This is essential for diagnosing issues like lean/rich conditions or oxygen sensor behavior.

Anonymous 2021-02-16 13:40

autojoe wrote: Tue Feb 16, 2021 11:27 am Your scan tool don't have data stream? My Torque Pro app on my phone does support some basic functions. I used this as a reason to purchase an Autel AutoLink AL519 OBD2 scanner for $60 on Amazon. It clears evaporation-related codes in my daily driver (a 2007 Solara convertible). My car hobby is restoring classic Fieros.

Anonymous 2021-02-16 14:14

I don't have extensive experience with budget-friendly or smartphone-based OBD2 tools. I own three high-end scanners—two standalone (Snap-on and Launch) and two laptop-connected units. While they cost a lot, updates are frequent and data streams are robust. Both real-time data and bidirectional controls are valuable for accurate diagnostics.