Code
P1189
GM
P — Powertrain
Engine Oil Pressure Switch Circuit
Views:
UK: 31
EN: 68
RU: 41
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the oil pressure switch circuit
- Corroded, loose or damaged connector at the oil pressure switch
- Faulty oil pressure switch or pressure sensor
- Low or no engine oil pressure (mechanical or oil pump fault)
- PCM or harness damage at the PCM connector
- Oil contamination of the sensor or connector
Symptoms
- Illuminated MIL (Check Engine Light)
- Stored P1189 and possibly related oil pressure codes
- Incorrect oil pressure reading on dash (if equipped) or erratic instrument behavior
- Engine may show low oil pressure warning or go into limp mode on some vehicles
- Possible oil leaks around sensor area
- Vehicle may not start or may run poorly if PCM limits performance due to fault
What to check
- Retrieve freeze frame and DTC history with a scan tool; note conditions when the code set (engine speed, temperature)
- Visually inspect oil pressure switch connector for corrosion, oil intrusion, bent pins or damage
- Inspect wiring harness along routing for chafing, pinches, heat damage or repairs
- Backprobe the switch connector and monitor live data or voltage with ignition on and engine off/running
- Check for related oil pressure codes (P0520–P0524) and pending codes
- Perform a mechanical oil pressure check with a calibrated gauge to confirm actual oil pressure (safety first)
Signal parameters
- Switch-type: expected continuity closed at low/no oil pressure and open at normal operating pressure (consult service manual for exact setpoint)
- Resistance: closed ~0–5 ohms; open >10 kΩ or infinite (typical for simple switches)
- If sensor provides voltage: reference voltage typically 5 V from PCM; expected output varies with pressure — 0–5 V range (refer to OEM chart)
- With ignition ON engine OFF: reference voltage present at connector pin; switch may pull signal to ground when closed
- With engine at operating pressure: switch state should change (open/closed) according to specification — verify with scan tool or multimeter
Diagnostic algorithm
- Read and record all codes and freeze frame data using a scan tool. Clear codes, then attempt to reproduce to confirm persistence.
- Visually inspect the oil pressure switch, connector and harness for damage, corrosion, or oil intrusion. Repair visible issues and retest.
- Backprobe the connector with the ignition ON and engine OFF. Verify reference voltage and ground presence per service manual. Note if the switch toggles when engine is cranked or started.
- With safe procedures, start engine (if allowed) and observe live data or measure voltage/continuity change as oil pressure rises. If switch does not change state, suspect switch or mechanical oil pressure problem.
- Perform a continuity check of the wiring from the switch connector to the PCM connector to locate opens/shorts or high resistance. Wiggle harness to check for intermittent faults.
- If wiring and connectors are good, replace the oil pressure switch/sensor and retest. Use correct OEM part and torque to avoid damage.
- If code remains after switch replacement, verify actual oil pressure with a mechanical gauge to rule out pump, relief valve, pickup screen or engine bearings as causes.
- If mechanical oil pressure is within spec and wiring/switch tested good, inspect PCM connector pins and test PCM outputs/inputs; consider PCM replacement only after all other causes eliminated.
- After repair, clear codes and perform a road test/idle check to ensure the code does not return and that oil pressure behavior is normal.
Likely causes
- Corroded/loose connector at the oil pressure switch
- Damaged wiring (chafing, broken conductor) between switch and PCM
- Faulty oil pressure switch/sensor
Fault status
Status
Engine Oil Pressure Switch Circuit — signal open/short/intermittent or out of expected range. Inspect switch, wiring, connector and oil pressure; confirm with mechanical gauge if needed.
Repair difficulty: Medium
Diagnostic time: 1–3 hours
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