The oil preassure sensor is located below the power steering pump near the firewall.
If you have no ses light on then the sensor must functioning and the pcm is reading the correct value. Your gauge might be faulty or the wiring harness maybe corroded, lose?
The sensor read 0.5 volts for 0 psi and 5 volts for 128 psi. At the sensor between the grey and the black wire you should read 5 volts and white/tan wire and black you should read something in between depending on the actual preasure.
The manual says to replace the instrument cluster if all the above check out fine?
You should get someone with a scanner to verify the oil sensors operation.
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