I get engen light when i put in to four wheel drive code po171

Question

when I put the truck in 4x4 it sometimes gives me the po171 code.

Answer 1

P0171 Fuel trim lean

When the you put the vehicle in 4x4 mode more fuel is needed. One of the most notable cause for this is when there is a reusable air filter that is over oiled. Do a MAF cleaning and it would not hurt to do a throttle body cleaning , the main cause that is always seen is the MAF sensor getting dirty.