Front HO2S heater resistance inspection

Disconnect the front HO2S connector.
Measure the resistance between front HO2S terminals C and D.
- If not within the specification, replace the front HO2S. (See HEATED OXYGEN SENSOR (HO2S) REMOVAL/INSTALLATION .)
1. Front HO2S heater resistance 1-10 ohms [20 °C {68 °F}]
  
  Fig 1: Identifying Front HO2S Connector Terminals
  Courtesy of MAZDA MOTORS CORP.

Disconnect the front HO2S connector.
Measure the resistance between front HO2S terminals C and D.
- If not within the specification, replace the front HO2S.
1. Front HO2S heater resistance 2-50 ohms
  
  Fig 1: Identifying Front HO2S Connector Terminals
  Courtesy of MAZDA MOTORS CORP.