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O2 Sensor 1 Voltage Compared to O2 Sensor 2 Voltage

Hi. I have a question regarding the operation of O2 sensor 1 (upstream) and O2 sensor 2 (downstream). Running a scan on the OBD 2 monitors and looking over the live data log of certain emission components, I found that oxygen sensor #1 had a voltage fluctuation much more than that of the 2nd (downstream) sensor, and it had more inconsistent reading of voltage output. I have no error codes and the check engine light is not on. Is this a sign that my O2 sensor is on its way out?

Answer:

Sounds like normal operation. In order for the catalytic converter to function correctly it needs a constant high and low of CO in the exhaust stream. That's what you are reading on the front oxygen sensor. The exhaust at that point should be switching from lean to rich and back (0.1v to 0.9v) around 60 times a minute. Now after the catalytic converter, the exhaust should be cleaned up of carbon monoxide (CO) and voltage should stay close to a steady 0.4v. posted by SmogTips Support

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