Oxygen Sensor (O2S) Testing

Fig. 21 Oxygen sensor output test:

Fig. 22 Manual operation of wide open throttle micro switch:

Fig. 23 Disconnecting vacuum hose to test oxygen sensor:

1. Start engine and allow to reach normal operating temperature.
2. Disconnect oxygen sensor connector.
3. Connect voltmeter between oxygen sensor side terminal and ground, Fig. 21. Use high quality or digital voltmeter. Do not apply any voltage to oxygen sensor.
4. With engine running at 1500 - 2000 RPM, turn wide open throttle micro switch on, Fig. 22. Voltmeter should read about .8 volts.
5. With engine running at 1000 - 1500 RPM, disconnect vacuum hose, Fig. 23, at intake manifold. Voltmeter should read almost zero volts.
6. Reconnect vacuum hose and electrical connector.