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"If values were false, I'd first check if the heater part of the O2 sensor was getting 12 V through the yellow-red wire before condemning it."
Over the years this has been the trouble for occasional 212 codes. The usual problem is fuse #4, either blown or just crusty on the ends, so my approach would be to simply check for battery on the fuse terminal on the right side of #4. This fuse protects the wiring to the oxygen sensor and to the tank's fuel pump. Neither the sensor's heater nor the tank pump is necessary for the car to be driveable.
Easy check and I'd put it in the first category. If the fuse is blown, the usual short is abraded wires at the oxygen sensor itself.
Second check would be the resistance measurement you suggest. To thoroughly check, warm the car for a few minutes. With ohmmeter at the ready, quickly disconnect the heater plug (the two white wires) and read the resistance toward the oxygen sensor.
A good one will start out at somewhere near 13 ohms and as it cools, slowly decrease to about 3-4 ohms. Watching it go through the heat cycle without interruption assures you the heating element isn't broken internally, which can be causing an intermittent connection.
--
Art Benstein near Baltimore
Why do banks leave vault doors open and then chain the pens to the counters.
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