Defective oil sending unit, blown bulb.
Check for power and ground to the sending unit . If you have that then ground the sending unit and see if it works.If the gauge works then the sending unit is defective.
Blown you'll pump fuse, defective fuel pump relay, fuel filter totally clogged, or fuel pump itself is defective.
It could be the cause.
Blown fuse, defective fuel pump relay, or a worn out fuel pump.
it is a defective speed sensor.
The oil pressure sending unit is defective.
A speedometer will stop working if the gauge has failed, the wiring is loose, or the sending unit has become defective. Each component must be tested to determine the cause.
it may be a defective sending unit or sensor.
Thermostat and/or heater core may be defective
There could be a problem with the power of common ground to the Cavalier light and sun roof. Check the fuses and wiring for the problem.
The most likely would be a defective fuel pressure regulator. An injector that is stuck open will also cause gas to get in the oil.