Circuit Description
WARNING: This page is about a different car, the 2002 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
The engine oil pressure switch is a normally closed switch that opens with the proper oil pressure. With the ignition switch turned ON and the engine not running, the PCM should detect a low signal voltage input. With the engine running, the pressure switch opens, and the PCM should detect a high signal voltage input. The PCM tests the state of the engine oil pressure circuit with the ignition switch turned ON, and the engine turned OFF. If the PCM detects a high voltage input on the engine oil pressure signal circuit, DTC P1189 will set.