HO2S Heater Inspection

Remove the battery cover. (See BATTERY REMOVAL/INSTALLATION [LF, L5] ).
Disconnect the negative battery cable.
Disconnect the HO2S connector.
Measure the HO2S resistance between terminals C and D.
- If not as specified, replace the HO2S.
  (See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION ).
  
  HO2S heater resistance 2-50 ohms [normal temperature]
  
  Fig 1: Identifying HO2S Connector Terminals
  Courtesy of MAZDA MOTORS CORP.