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Oxygen sensor testing waqrning

Maybe everyone knows but me?


An oxygen sensor must be tested with a digital voltmeter. If an analog meter is used for this purpose, the sensor may be damaged.

I hadn’t heard this. (I only own a digital multimeter, so I’m safe regardless.) Where did you find this out? Not from unhappy experience, I hope.

This is absolutely true. Furthermore, even a digital voltmeter will not tell you everything you need to know. The failure mode for an oxygen sensor usually starts with the response time getting slow. You cannot detect that with a multimeter. Only an oscilloscope will tell you if response time is getting slow and it is time to replace the sensor. A voltmeter will show you changing voltage the corresponds to the sampling rate of the meter. That will tell you only whether the sensor output voltage is low or gone completely.

This warning comes from the early '80s when cars were first becoming computerized. Some delicate solid-state modules were supposed to be susceptible to the battery output of an analog instrument. I heard the statement but never took it too seriously.

We’ve come a long way since then. And considering that an oxygen sensor is not a delicate device, no complex circuitry, I would take any such warning with a grain of salt. However, heed Manolito’s advice about proper testing using the oscilloscope.

That’s true and while O2 output can be tested to some extent with a digital VOM one should not perform a resistance check on an O2, even with a digital VOM.

Read it on

To avoid possible damage to the engine computer, or any other electronic devices, use a HIGH IMPEDANCE DIGITAL MULTIMETER.

Analog multimeters (“voltmeters”), and low impedance digital multimeters, can damage modern (and, “old”) electronics. The chief damage is from the battery in the analog (needle indication) meter, which is usually 9 volts dc. Electronic circuits operate on 5 volts dc, or less. The circuit which senses the output from the oxygen sensor is sensitive to voltage of 0.1 volt to 1.0 volts. Voltage greater than this can damage these circuits.

Using the OHMS scale testing with an analog meter would send 9 volts dc through these low-voltage circuits; resulting in possible ZAP! ZAP!
Don’t fry your electronics (or, chance it) use high impedance digital voltmeters.