P0171 2002 MERCURY SABLE DOHC 3.0

Question

The engine light came on but the motor seems to run just fine. Any clue?

Answer 1

P0171 Fuel trim lean Bank 1

Vacuum leaks are common causes, check the PCV hose for any rupture  hose which would cause false air leak.

 Vacuum hose such as the hose on the PCV are common places to look for vacuum leaks as well as its vacuum hoses.