"Should reading constantly show a value within the range."

No. When the sensor is connected, and everything is working right, you should see a rapid flashing of numbers. That's the sign of the sensor and ECU working together to keep the mixture in the correct range (a nominal 0.5V).

But that 0.5V is a "knife edge" goal, and the mixture strays on either side. The O2 sensor tells the ECU which way it's off by raising or lowering it's voltage output, and the ECU responds by making the appropriate correction. This cycle repeats at a rapid rate, hence the flashing numbers.

My criteria for O2 sensor metering is to see most of the numbers in the .3 to .7 range, with an occasional .2 or .8 and no .1s or .9s (well, maybe very rare .1s or .9s).

It's not easy to read the numbers with a good sensor, you just try to scan for those extremes. If the numbers flash slowly, its probably because the sensor is old and slow.


--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.