Possible causes

– Bank 1 Sensor 1 / Bank 2 Sensor 1 harness is open or shorted
– Bank 1 Sensor 1 / Bank 2 Sensor 1 circuit connectors (wrong connection)
– Faulty Engine Control Module (ECM)

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0040 FORD Description

The heated oxygen sensor (HO2S) monitor determines if the HO2S signal response for a fuel shift corresponds to the correct engine bank.