This DTC is a very common issue on the V6 and refer at the little rubber elbow on the PVC wears through.
P0171 - System Too Lean (Bank 1)
P0174 - System Too Lean (Bank 2).
Those lean codes are for a lean fuel condition. The first thing I would
check is for a vacuum leak. Especially look around the PCV system. Look
for soft or collapsed hoses in the PCV system, (especially the rubber
elbows) these are very common issue for failure and cause of lean codes.
Also check around the intake manifold for leaks or any other hoses that
may have come off.
Next I would check fuel pressure and the fuel filter
for blockage. If the filter is old you might as well replace it. If and
when you find an issue you will have to have a scan tool to reset the
check engine light before you go back through emissions.
Check that
stuff and let us know what you find.