Unplug the oxygen sensor's harness connector so that the oxygen sensor is no longer connected to the computer and the feedback control system is in open loop control. Connect the positive pen of the multimeter's voltage file directly to the oxygen sensor feedback voltage output terminal, and the negative test lead is well grounded. When measuring the feedback voltage during engine operation, first disengage the crankcase forced air pipe or other vacuum hose connected to the intake pipe, artificially form a lean mixture, while watching the voltmeter, the pointer reading should be lowered.
Then connect the disconnected pipe, then pull off the water temperature sensor connector, replace the water temperature sensor with a 4-8KΩ resistor, artificially form a rich mixture, and watch the voltmeter, the pointer reading should rise. It is also possible to change the concentration of the mixture by suddenly pressing or releasing the accelerator pedal. When the accelerator pedal is suddenly depressed, the mixture becomes thicker and the feedback voltage should rise. When the accelerator pedal is suddenly released, the mixture becomes thinner. The feedback voltage should drop. If the feedback voltage of the oxygen sensor does not change as described above, it indicates that the oxygen sensor is damaged.
In addition, when the titanium oxide type oxygen sensor is detected by the above method, if it is a good oxygen sensor, the voltage at the output end should fluctuate up and down around 2.5V. Otherwise, the sensor can be removed and exposed to air, and its resistance value measured after cooling. If the resistance value is large, the sensor is good, otherwise the sensor should be replaced.