Starting at the beginning...
The engine burns a combination of fuel and air - in fact, gasoline will not even burn all by itself, it requires the presence of some air.
The engine computer controls the mixture / ratio of how much air and how much gas is perfect at any given time.
All those sensors that you find all over today's car are feeding information to the computer - things like the temperature of the air, the barometric pressure, the temperature of the engine coolant, how much oxygen is in the exhaust, and so on.
Based on all this information, the computer will adjust the mixture to more fuel, or less fuel, more air or less air.
Sometimes the computer gets it wrong based on something is starting to go wrong with some part of the system.
Another situation that is very common that results in the mix being wrong is when air is sneaking into the system, bypassing the sensors in a way the computer doesn't know the extra air is even there.
When you hear the term "vacuum leak", that's a reference to air sneaking in through a broken rubber hose, a seal that has hardened and shrunk, or a dozen other situations.
When there is too much fuel in the mix = "rich condition".
Not enough fuel, or conversely, too much air = "lean condition".
If you are getting a Lean code then it is probably being caused by the intake plennum gaskets. This is a common problem on the Windstar. The fix is relatively easy.
There is a known problem with the 3.8 engines in 1999-2003 Windstars.See "Related Questions" belowAnswerI was just told today that my 2000 Ford Windstar is running lean, too. He said it's most likely a vacuum seal problem so i was told to change my PVC valve and my plenum gasket
Could be sucking air into intake.
Running lean basically means that your Air Fuel Ratio is off and there is more air than fuel, which creates a lean condition. It is called the "Stoichiometric" value. The correct ratio is 14.7 parts air to one part fuel. If you are running for instance a ratio of 16 to 1 then that is lean. Basically too much air when compared to optimal air fuel mix. A ratio of 12 to 1 is too rich. The problem with a lean condition is that the engine will run hot. Normal logic would suggest that with less fuel there would be less heat generated, but it is not the case. A lean condition will actually make the engine run hotter.
Bank 1 is the passenger side of the engine , engine cylinders # 1 , 2 , and 3 Bank 2 is the drivers side of the engine , engine cylinders # 4 , 5 , and 6 firewall 3 - 6 2 - 5 1 - 4 front of Ford Explorer ( V6 ) The fuel mixture for the engine is running lean ( there is not enough gas in the air / fuel mixture )
That code is telling you that bank two is running too lean. For some reason the fuel mixture is too lean. Possibly an o2 sensor is malfunctioning.
Trouble code P0171 means:System too lean (Bank 1)
engine is running lean while eccelerating
Perhaps a clogged fuel filter.
A faulty fuel injector can cause your Ford Windstar to run rough and feel like it's going to stall. A dirty or plugged air filter can also cause the vehicle to stall.
Trouble code P0171 means:System too lean (Bank 1)
Engine is running lean.