A/F Sensor Heater Inspection

Remove the battery cover. (See BATTERY REMOVAL/INSTALLATION [L3 WITH TC] ).
Disconnect the negative battery cable.
Disconnect the A/F sensor connector.
Measure the resistance between A/F sensor terminals 2B and 2D.
- If not as specified, replace the A/F sensor.
  (See AIR FUEL RATIO (A/F) SENSOR REMOVAL/INSTALLATION .
  
  A/F sensor heater resistance 1-10 ohms [normal temperature]
  
  Fig 1: Identifying A/F Sensor Connector Terminals
  Courtesy of MAZDA MOTORS CORP.