Mazda A/F harness chafe
Some Mazda vehicles (2007-2009 Mazda3 and 2007-2010 Mazda5 produced before Nov. 6, 2009), may experience the MIL on with DTC P0131/P2251 because the A/F sensor connector bracket contacts and damages the sensor harness. To prevent interference, the shape of the sensor connector bracket has been changed.
DTC P0131: A/F sensor circuit low output
DTC P2251: A/F sensor negative current control circuit open
Inspect the A/F sensor harness for damage. If the harness is damaged, bend the sensor harness connector bracket to prevent interference, than replace the A/F sensor.
Note: be sure to cover the tips of pliers with vinyl tape to prevent damaging the bracket surface (to prevent future rusting).
Using pliers, bend the bracket to create 8mm or more clearance between the harness and the edge of the bracket.