1999 Plymouth Voyager oil light

Hi:
When the car is ideling in gear, it's at the lowest RPM it will be used which causes the oil pressure to drop. However, the gauge and light shouldn't come on for you. If you have replaced the sending unit and the problem still is there, you need to have the pressiure tested by a mechanic that has the correct tools. If the pressure is too low, eventually it will cause internal engine damage.

Considering you have 125K on the van, the oil pump screen could be getting plugged or the pump may be going bad.

Let me know if you have any other questions.

Joe