The OP has a 2000 XJ. The oil pressure sensor is similar to the variable resistor sensors, like the MAP Sensor and the TPS. See diagram of the TPS circuit below.

If there is high resistance in the 5 volt supply voltage the signal output to the PCM will be low. If there is low-no resistance in this circuit there will be no change in the supply voltage, or voltage from the TPS to the PCM.

If there is high resistance in the signal circuit to the PCM the PCM will receive a low voltage signal. If the signal wire is shorted to voltage the PCM will receive a high voltage signal.

The PCM receives voltage signals from the TPS (in this case, the OPS) and routes the voltage signals through the CCD Bus to the instrument cluster. The microprocessor in the Instrument Cluster interprets the inputs and drives the electro-mechanical oil pressure indicator.

Somewhat different than the RENIX system I'd say.

 

This.

I've also had multiple bad senders on our 2000.

Got to the point where i just threw a mechanical test gauge on it to make sure it wasn't eating itself. It wasn't.

And now i don't even care about what the stock gauge says. If it's truly got 0psi at hot idle, then i'd hear something pretty awful going on.

 

Wow, different indeed! The Renix oil pressure monitoring system is the same as systems have been forever ... a sender connected to a gauge by a wire.