4.3 MPI One beep every second

[danaa]

Once my engine reaches normal operating temp, 165 degrees or so, I get a constant one beep per second. Engine does not overheat. Outdrive oil reservoir is full. Disconnected the raw water pressure sensor, no change. Haven't disconnected the oil reservoir sensor yet. Any thoughts on what could be the cause?

 

[Fun Times]

Possibly a bad water temp sensor that is out of range and once you hit 165, the ECM thinks it at 196+ degrees sounding the waning horn....Possibly.....

This sensor should/may have a yellow and black wires running to it. Problem is if you just disconnect it from the sensor, it could also sound the warning horn falsifying a warning horn test and a reading should someone connect a scan tool up to read fault codes.
Best to try ohms checking the sensor in hot water and compare it to the ohm values found in the service manual that I posted below for you.

Approximate temperature to resistance values:
Water Temperature - Ohms Reading:

-40°F (-40°C) : 100,700 ohms

0°F (-18°C) : 25,000 ohms

20°F (-7°C) : 13,500 ohms

40°F (4°C) : 7,500 ohms

70°F (20°C) : 3,400 ohms

100°F (38°C) : 1,800 ohms

160°F (70°C) : 450 ohms

210°F (100°C) : 185 ohms

Or here is a voltage check for reference.
http://www.aa1car.com/library/coolant_sensor_chart.gif