First of all to ensure the use of Cummins generator specified pure engine oil, check the failure generally follow the principle from simple to complex.
Check the oil pressure gauge is damaged, the reading is accurate, if the oil pressure gauge has a problem to replace the oil pressure gauge, if no problem check the next step.
Check the oil pressure sensor sensitivity, if the oil pressure is not high, it leads to the hydraulic readings are not accurate, should replace the oil pressure sensor, if not, we can check the next step. Check the oil level, oil viscosity, oil quality is in line with the requirements. Check the oil pump suction, if the oil pump suction is not enough to replace the oil pump.