Heated Oxygen Sensor (Ho2S)

WARNING: This page is about a different car, the 1995 Mazda B4000, 1995 Mazda B3000, and 1995 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: HO2S is located in exhaust pipe, upstream of the catalytic converter. Faults in sensor or circuit should set a service code. See appropriate TESTS W/CODES article.

To test sensor, warm engine to operating temperature. Unplug sensor. Connect DVOM positive lead to Gray/Light Blue wire (Red/Light Green on some sensors) on HO2S. Connect DVOM negative lead to Orange wire on HO2S.
Start engine and run at high and low speeds while monitoring voltage. Voltage should fluctuate between 0.2-1.0 volt. If voltage is not as specified, replace sensor.
To check sensor heater, measure resistance between remaining 2 terminals. With sensor at room temperature, resistance should be 2-5 ohms. With sensor warm to hot, resistance should be 5-30 ohms. If resistance is not as specified, replace sensor.