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2004 Ford Taurus 3.0L V6 P0174 and P0191: Check Engine Light On, Loss of Throttle Response at Highway to City Speed Changes

Model: 2004 FORD TAURUS Fault Code: P0174 Posted: 2006-04-16 23:56

I have a 2004 Ford Taurus with a 3.0L V6 engine. Recently, the check engine light came on, and I noticed a severe loss of throttle response—especially when transitioning from highway speeds (70–75 mph) to city driving (30–40 mph). The engine continues to run but provides little or no power during these transitions. This issue only occurs during rapid speed changes. After turning off the ignition for 20 seconds and restarting, the car returns to normal operation temporarily. I've already replaced the fuel rail pressure sensor, fuel filter, and air filter, but the problem persists. Diagnostic trouble codes pulled show a 'Fuel Rail Sensor Input Voltage High' and a 'Bank 2 Lean' condition. Despite these repairs, symptoms reappear under specific driving conditions. Could this be related to fuel pressure fluctuations or a vacuum leak? I'm seeking advice on how to properly diagnose and resolve the P0174 and P0191 codes in my 2004 Ford Taurus 3.0L V6 engine. Any insights would be greatly appreciated. Thank you, EAGLES1

Related fault codes

P0174P0191

Comments (3)

Anonymous 2006-04-17 17:09

First, verify that the fuel pump driver module is functioning consistently—check for intermittent shutdowns. If possible, borrow a known-good unit and test it. Use a fuel pressure gauge to measure actual rail pressure at the fuel rail and compare it with the sensor reading. To get an accurate reading, you'll need to remove the vacuum line connected to the fuel rail sensor. The symptoms suggest either a failing fuel pump driver module or inconsistent fuel pressure. Fixing this should resolve both P0174 and P0191 codes. If the P0174 code remains after addressing this, inspect for vacuum leaks around the PCV valve hoses and intake manifold. Good luck—please keep me updated. Jeff

Anonymous 2006-04-19 00:27

Update: The issue only occurs when the engine is warm. I drove all day without any problems, and I didn’t have the AC on. It seems the problem appears specifically when the A/C is running. This could point to a temperature-related fuel system or intake leak. I’m now considering whether the fuel pump might be failing—especially under warm conditions. I’ve also noticed that gaskets and valves may need inspection, but I don’t have much time due to working two jobs. I’ll check these components over the weekend. Thank you for your help—I’ll keep you posted. Have a great day!

Anonymous 2006-04-28 08:04

Here are some additional troubleshooting ideas: - A dirty fuel tank may require multiple filter changes before clearing up; in such cases, consider removing the tank and flushing it completely. - Check for kinked plastic fuel lines—these can bend or collapse when the vehicle is warmed up (e.g., after bottoming out on a curb), especially during highway driving. - A blocked tank vent may cause pressure issues. Try running the car with the fuel cap off (this will trigger evaporative codes but won’t affect engine performance). - Ensure your vehicle has the latest software update—this is typically provided by Ford dealers and is often free. - Fuel pumps can weaken over time, especially after long drives; they may become 'anemic' under load or heat. The most effective diagnostic step is to install a semi-permanent fuel pressure gauge (such as an Autometer electric sender) and monitor pressure during symptom occurrence. A mechanical gauge works too—but be cautious with live fuel lines in the cabin. - If you have a reliable voltmeter, connect it directly to the fuel rail sensor to monitor its signal to the PCM—expect readings between 0–5 volts. - Occasionally, using winter blend fuel on warm days (e.g., climbing a mountain) can cause temporary fuel pressure loss due to temperature changes.