P1189 CHEVROLET - Engine Oil Pressure Switch Fault
- Engine Oil Pressure Switch harness is open or shorted
- Engine Oil Pressure Switch circuit poor electrical connection
The low oil pressure sensor is normally closed. When oil pressure increases above 1 to 4.5 psi the switch contacts open. The Powertrain Control Module (PCM) supplies 12 volts to the oil pressure input circuit. With low oil pressure the 12 volts is pulled low to ground. This diagnostic tests for a open condition of the oil pressure switch circuit. If the engine has been off long enough for engine temperature to drop by 10°C, then a shorted (low oil pressure) condition of the circuit should be observed prior to engine running.