Its a problem with that sensor, or the wiring. The next step is to unplug the PCM, and test the resistance between B14 and B15 with the sensor plugged in. The reading should be the same as your first resistance reading.

 

I recently had a persistent code 9 (faulty CYP sensor on my 94EX. As you did I measured resistance at the sensor (800 ohms. in spec). As PA suggests, I next checked resistance at the ECU connector, and got same values. This indicated a fault in the ECU itself, which was resolved w/ a used ECU. You could have a similar problem, but a wiring fault is still possible.

good luck

 

After you measure resistance at those pins at the ECU, next check whether there's any continuity to ground on either of those wires. (shouldn't be any continuity to ground)