496 MAG HO alarm due to low oil pressure. true or bad sensor?

have a constant single beep alarm going off once I hit about 2000 rpm and power drops down to 10%. received my scan tool today and it shows me this is due to low oil pressure, which the scan tool shows at 3.1 psi.

my dash gauge always shows between 38 to 40 psi. which one do I believe? I know the water temp sensor is one that seems to be giving many merc owners false readings (bad sensor) but is this the case with the oil sensor?

If I did have that low of a pressure wouldn't I also be overheating? my temp stays at a constant 170. could a quart low cause this?

If I disconnect the sensor I get no alarm so before I purchase new sensor Im wondering if there is a good way to test this one. scan tool says it test sensors but I can not see how.

would anyone know the part # of the oil pressure sensor?

and what size socket to remove this one. very tight space. can only feel it.

best thing to do is to get a mechanical gauge, of known accuracy, and make sure you know how much oil pressure is being delivered....this is one you don't want to do by trial and error. Usually a v-8 with only 3 psi in the galley will be very noisy, especially in the valve train, even with a roller cam - still be to check via a known gauge.

Sensor failures being "off" but still in a valid range are the most frequent type of failure mode.

You can get the part number by looking it up a mercruiserparts.com, if you have the serial number.

One way to "test the sensor" would be to remove it and couple it to a regulated compressed air source. plug in the connector, turn on the key, and see what the scan tool displays for oil pressure. change the pressure and see if the scan tool output tracks what the regulator shows....not quick or easy but foolproof

First, make sure oil level is full. If still no reading.
I would be looking to get a mechanical guage hooked up to the engine.
Some engines have a threaded port beside the oil filter to do this.
Typicaly the first mechanical sign of no oil pressure is the top of the engine.
You will hear the valve train rattle.
Look into the valve covers with engine cranking, you should see oil flowing on top of the head.
If you have no way to get a guage on it, you could put a pin hole into the oil filter, You could see how bad oil squirts out, then replace the filter.

This is not something to mess around with for very long. Pull the wire from the coil so the engine will not start, and do all testing with the starter spinning the engine only.

With the proper water flow, the temp would not go up.