If the oil pressure light comes on in a 2002 toy corolla with good oil level what is the problem?

Low oil pressure is typically caused by worn main and/or rod bearings. If the oil level is up the problem is almost always the bearings. Rod and main crankshaft bearings ride on a thin film of pressurized oil. Once the bearings wear out the gap between the crankshaft and the bearing increases, allowing the pressurized oil to leak out. The pump cannot produce enough volume to keep the pressure up, then the pressure drops and the sensor turns on, indicating that you have a problem. Try switching to a heavier grade oil. That will be thicker oil which does not leak out as fast. Pick an oil with higher viscosity numbers to see if you can get the oil pressure to go a little higher.