Hello. My friend has a 2000 Jeep Grand Cherokee 4.0L with 242k miles. The oil pressure gauge reads 0 PSI at idle, and the check engine light comes on. The oil level is full, and the pump is working (confirmed by a shop). When he accelerates, the OP rises to around 40 PSI and immediately as the gauge moves away from 0 the CEL goes off. Could this be the oil pressure sending unit, or symptoms of excessive wear elsewhere?