Heated Oxygen Sensor (Ho2S)

1. Warm engine to normal operating temperature. Disconnect oxygen sensor connector. Connect voltmeter negative lead to HO2S terminal "B". See Fig 1 . With engine running at idle, voltage at terminal "A" should be fluctuating at less than one volt. While accelerating engine, voltage should be .5-1.0 volt. While decelerating engine, voltage should be .1-.4 volt.
2. To test oxygen sensor heating element, let sensor cool to room temperature. Disconnect HO2S connector. Measure resistance across terminals "C" and "D". See Fig 1 . Replace sensor if resistance is not 6-13 ohms at 68°F (20° C).

Fig 1: Identifying HO2S Terminals

Courtesy of MAZDA MOTORS CORP.