I took my truck (1996 F-150 4x2 / Straight 6) to Auto Zone to have the codes read from the OBD2 port. The following codes came up, and I'm trying to figure out where to start! Can anyone direct as to what the first step should be in regards to replacing components? There are quite a few, and I would hate to spend money on an item that is functioning properly!

Codes:
PO411 (Secondary Air Injection System Incorrect Flow Detected)
PO401 (Exhaust Gas Recirculation Flow Insufficient Detected)
PO171 (System too Lean (Bank 1)
PO174 (System too Lean (Bank 2)

Thank you in advance for your help!!!!

 

PO401 may be as simple as the tube between the EGR & the exhaust manifold is plugged up & needs to be cleaned.
As for the rest, I'll let the real experts answer those.
AL.