P0171 2006 Ford Fusion -

Question

The solutions listed to this error are Air Filter or MAF or Front O2 sensor replacement. But it does not specify WHICH O2 sensor to replace. It is my understanding there are four, 2 in Bank 1 and 2 in bank 2.

Answer 1

 

P0171 Fuel trim system lean Bank 1

This would not be a MAF (mass airflow) unless it has P0174. If you have Both P0171 and P0174 then yes the MAF should be check, but before you replace any parts a visual inspection is needed, Most lean code condition are caused by vacuum leaks, Vacuum leaks are air that gets past the MAF and is unaccounted for.

 Here is lean code , what was found was a disconnected vacuum hose, this was a easy find becuase you can hear, this hose connection  which connected to the throttle body. 

 

 Another cause of lean code condition are the MAF , All airfilter that are on the market. must have a fire retardant applied to the filter, In return what this does is prevent air filter from catching on fire.it also coats the MAF and prevent a proper metering of measuring the air that enter the engine. Doing a MAF cleaning usually resolves the problem of lean code conditions