You will need a high impedance, Minimum 10 Meg (10,000,000) ohm input impedance, Digital Volt Ohm Meter (DVOM) to test the HO2S.
1. Make sure the vehicle is at normal operating temperature. Run the engine at 2,500 rpm for 3 minutes with the transmission in PARK (A/T) or NEUTRAL (M/T).
2. With engine OFF, connect the negative lead of the DVOM to engine ground. Set the DVOM to read DC VOLTS. Disconnect the oxygen sensor (O2S) electrical connector and connect the positive lead of the DVOM to the oxygen sensor signal wire (black/dark green).
3. Start engine. Create a lean condition for 10 seconds . Voltage should decrease to 0.2 volt or less and remain there.
4. Create a rich condition for 10 seconds. Voltage should increase to 0.8 volt or more and remain there.
5. If sensor fails to vary according to the test steps above, the sensor is defective.
6. Connect sensor and clear codes.
If it passes this test then you will have to look at the wiring and a possible bad PCM. There is only one HO2S in the system.
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