I am having a similar problem with mine. The original oil sender was bad and I replaced it, however the icon and buzzer continue to beep. You can check the sender with a voltmeter to check the resistance with the floats in different positions.
Try unplugging the oil sender connector, then shorting the wires at the connector on the display end. Then try startiing it. If it doesn't beep, the sensor may be bad. if it does beep, the shop manual says you replace the display. They are very expensive, $500 for a 2001 model. Unless there is someone out there who can repair one.
If you have the sender out, clean the filter too (the mesh tube on the outside).