DTC P1189: Engine Oil Pressure Switch Circuit: Testing

1. If instrument cluster diagnostic system check was performed, go to next step. If instrument cluster diagnostic system check was not performed, see INSTRUMENT CLUSTER DIAGNOSTIC SYSTEM CHECK  under DIAGNOSTIC SYSTEM CHECKS.
2. Turn ignition on. Connect a scan tool. See Figure. Observe ENGINE OIL PRESSURE SWITCH parameter in PCM ENGINE DATA 3 list. If ENGINE OIL PRESSURE SWITCH parameter does not indicate LOW, go to next step. If ENGINE OIL PRESSURE SWITCH parameter indicates LOW, check for faulty connections in oil pressure sending unit circuit.
3. Turn ignition off. Disconnect engine oil pressure sending unit. Connect a fused jumper wire (3-amp) between ground and oil pressure switch harness connector terminal "A" (Brown wire). See Fig 1. Turn ignition on. Observe the ENGINE OIL PRESSURE parameter on scan tool. If ENGINE OIL PRESSURE parameter does not indicate LOW, go to next step. If ENGINE OIL PRESSURE parameter reads low, go to step  5.
4. Check for an open in Tan/Black wire between oil pressure sending unit harness connector terminal "A" and Powertrain Control Module (PCM) 80-pin harness connector C2 (Clear) terminal No. 20. See Figure and Fig 1. If no problem was found, go to step  7. If a problem was found and corrected, go to step  10.
5. Check for an open in Black wire between oil pressure sending unit harness connector terminal "B" and ground G100 located at left front corner of engine compartment. If no problem was found, go to next step. If a problem was found and corrected, go to step  10.
6. Check for faulty connections at oil pressure sending unit. If no problem was found, go to step  8. If a problem was found and corrected, go to step  10.
7. Check for faulty connections at PCM harness connector C2 (Clear). If no problem was found, go to step  9. If a problem was found and corrected, go to step  10.
8. Replace engine oil pressure sending unit. See OIL PRESSURE SENDING UNIT  under REMOVAL & INSTALLATION. After replacement go to step  10.
9. Replace PCM and reprogram. See POWERTRAIN CONTROL MODULE under REMOVAL & INSTALLATION in BODY CONTROL MODULES - DEVILLE article. After replacement go to next step.
10. Use scan tool to clear DTCs. Operate vehicle within conditions for setting DTC. If DTC does not reset, system is okay at this time. If DTC resets, return to step  2.

Fig 1: Identifying Oil Pressure Sending Unit Harness Connector Terminals

Courtesy of GENERAL MOTORS CORP.