Question about Ford F-150
P0174 and P0171 mean that there is too much air in the fuel/air mixture injected into cylinders.
You get the two codes for the two banks of cylinders as soon as the problem is detected through the O2 sensors.
There are many cause that can trigger this two codes, the possible reason can be better found observing any other symptom.
If the truck drives regularly, but you get the codes, then check the MAF sensor. The MAF determines the amount of air getting into the intake. MAF malfunctions can easily trigger lean codes.
If the MAF is dirty, try cleaning it, otherwise replace it.
If there are idle problems, check AIT (air intake temperature), and IAC (idle air control) valve. Both parts influence amount of air to be mixed when idling.
If the car is revving erratically or shutting down, check EGR valve. The EGR valve opens and close to use recirculated gas in the mixture EGR malfunctions will cause a number of problem, and often a lean code.
The DPFE sensor connected to the EGR valve may also cause the problem.
Under all conditions, check the vacuum system for leaks. A vacuum leak willl allow more air into the mixture returning a lean code.
The vacuum is tested using a hand gauge in the vacuum lines while heating lines at same time. Big leaks can be spotted because of hissing noise.
See: Actron Vacuum Gauge, Fuel Tester - 2179
In some occasion a faulty fuel pump or a clogged fuel line can prevent gas from being mixed to air, causing the lean code. Fuel circulation is tested with same tool used on vacuum.
I think I listed the most common reasons for a lean code. Start from vacuum and fuel, and if they are OK try replacing the MAF. This are very common faults that may store a lean code in the PCM memory.
Posted on Jun 03, 2010
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Posted on Jan 02, 2017
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