From our DTC stickie at the top of this page:

P0171 - System to Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. For lean and rich DTCs:
Fuel system
Excessive fuel pressure.
Leaking/contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Vapor recovery system.
Induction system:
Air leaks after the MAF.
Vacuum Leaks.
PCV system.
Improperly seated engine oil dipstick.
EGR system:
Leaking gasket.
Stuck EGR valve.
Leaking diaphragm or EVR.
Base Engine:
Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2Ss.
A SHRTFT-1,2 PID value between -25% to +35% and a LONGFT-1,2 PID value between -35% to +35% is acceptable. Reading beyond these values indicate a failure.


Vacuum leaks are the most common, wherever they occur. A forgotten cause is an exhaust leak that can affect the O2 sensor readings.

Your model uses a special multi-layer gasket between head and exh. manifold, with passages for the Air injection as part of the gasket. So be careful to use the right type to maintain air injection capability if replaced.

Have you checked fuel pressure with a scan tool? Reset CEL DTC's and rechecked when they appear again?

 

Thanks for the reply.
We have reset the CEL codes and each time they come back again with the P0171 code. It usually takes a couple of days for the CEL to return.
I am not familiar with how to check the fuel pressure with a scan tool. Is that something that can be done with the local auto parts store scanner, or is a more sophisticated scanner required?

 

Parts stores typically only read codes, though it doesn't take a very fancy scan tool to see more than just that.