Both P0171 and P0174 are OBD II Trouble Codes, also known as Fault Codes.
P0171 indicates the passenger side cylinders (bank 1) on your Ford Explorer
are running lean. P0174 indicates the driver side cylinders (bank 2) are
running lean as well. So basically your Ford's engine is running lean; it's
not getting enough fuel... OR it's getting too much air. Now this could be a
mechanical problem or an electronic one. The oxygen sensor in both banks 1 &
2 have detected a lean fuel condition (too much oxygen in the exhaust).
If the problem is mechanical two things to look for are vacuum leaks (loose,
cracked, disconnected vacuum lines), and/or faulty fuel pump or fuel filter.
If the fault is electronic, the first component to suspect is the MAF (Mass
Air Flow) Sensor. The Mass Air Flow sensor may be dirty or defective. The
MAF sensor sends the engine control computer data about the amount of air
entering the engine. Using this information the ECC can determine how long
to keep the fuel injectors open per intake stroke, thus controlling air/fuel
mixture.
