how to fix error code po401 and code po171 on 1999 f150 4.6 motor
PO171 is lean code for bank 1. PO401 indicates the computer has determined Exhaust Gas re-circulation is insufficient. Check the net for Ford vehicles which experience both codes as once. Saw a couple of videos which may be of help.
Check for clogged ports on the EGR valve. The passageways get carbon-like deposits that block the EGR valve.
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