Possible causes
– HO2 sensors harness is open or shorted
– HO2 sensors circuit fuse
– HO2 sensors circuit relay defective
– HO2 sensors circuit connectors (wrong connection)
– Faulty Engine Control Module (ECM)
– HO2 sensors circuit fuse
– HO2 sensors circuit relay defective
– HO2 sensors circuit connectors (wrong connection)
– Faulty Engine Control Module (ECM)
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P0040 MAZDA Description
The heated oxygen sensor (HO2S) monitor determines if the HO2S signal response for a fuel shift corresponds to the correct engine bank.