Lean bank one and lean bank two trouble codes at the same time? Is your Ford, Lincoln, or Mercury vehicle inhaling more gas than a Hummer H2? Before you even think that both oxygen sensors have gone bad simultaneously, consider this, you have a better chance of getting struck by lightning.
In other words, don't pull out big money at your local parts store counter just yet. Nine out of ten times, P0171 and P0174 are caused by a simple glitch in all Ford, Lincoln, and Mercury vehicles equipped with 4.2L V6, 4.6L V8, 5.4L V8, and 6.8L V10 engines.
Clean your mass-airflow (MAF) sensor! The sensor itself usually acquires a layer of build-up from dust, debris, and other deposit particles causing the dirty leads to give the car's PCM incorrect readings for fuel and air mixture ratio. This occurs under normal driving around every 6,000 miles.
There are two hot wire leads that provide this function on the MAF. To access the sensor, you will need a bottle of mass-airflow cleaner and a "tamper proof" aka Torx bit (size 20). Unplug the wiring harness connector. Loosen the two Torx head screws.
Gently pull out the sensor from the intake housing. Be careful as the plastic is fragile. Excessive force may damage the wires. Now take a look at the double leads. I bet you they "appear" to be normal. Wrong. Spray the MAF cleaner onto the leads and watch the transformation as the substance drips off.
Now that the hot wire leads are all shining like chrome, reassemble. Undo negative battery terminal for 5 minutes. This is going to clear the "check engine" light. After reconnecting the battery, proceed to start the engine. The engine is going to stall out immediately. Restart it. Engine will die again. Restart it one more time.
Notice the improved idle quality and more appropriate idle speed? Leave the engine on for at least 3 minutes so the PCM can "re-learn" itself. You will see a significant gas mileage improvement, throttle response, driveability, and best of all, no more "check engine" light.
This is a popular trouble spot 90% of the time, even often overlooked by many experienced technicians. However, if your "check engine" light comes back on after cleaning the MAF, you may have a 10% of the following conditions: PCV hose vacuum leak or PCV hose collapsed at rear of intake plenum, sticking EGR valve, fuel injector leak, weak fuel pump, or faulty fuel pressure regulator.
Hope this helps all you Blue Oval guys out there.