Code
P1189
CADILLAC
P — Powertrain
Engine Oil Pressure Switch Circuit
AI status
Completed
Completed
100%
Causes
- Faulty oil pressure switch (open or shorted)
- Wiring damage (open, short to battery, short to ground, or high resistance)
- Poor connector contacts or corrosion at the switch or PCM connector
- Low engine oil level or severely degraded oil
- Restricted oil passages, failed oil pump, or internal engine wear causing low pressure
- Intermittent connection caused by vibration or heat
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- DTC P1189 stored (may be accompanied by other oil pressure codes)
- Oil pressure warning lamp or message (on some models)
- Possible poor engine performance or limp-in mode (rare; depends on calibration)
- Noisy engine or low oil pressure confirmed on gauge
- Intermittent warning or MIL
What to check
- Check engine oil level and condition; top up to spec if low and retest
- Scan for stored/related DTCs and freeze-frame data; note conditions when fault set (rpm, temperature, oil temp)
- Visually inspect wiring and connectors at the oil pressure switch and PCM for damage, corrosion, loose pins or bent terminals
- Check fuses and related power/ground circuits for the PCM/sensor
- Backprobe the oil pressure switch connector and monitor the signal while cranking and running (see signal params below)
- Measure continuity and resistance between the switch terminal and PCM pin (with ignition off)
Signal parameters
- Note: exact voltages/thresholds vary by model year — confirm with factory service data before final decisions.
- Typical switch behavior (example only): switch closed (low oil pressure) = near 0–1.0 V; switch open (normal pressure) = ~4–5 V (or open-circuit to PCM pull-up).
- Resistance: closed = near 0–5 Ω; open = large resistance/OL (infinite).
- Typical switch trip threshold (example): closes below roughly 5–15 psi (manufacturer-specific).
- When engine is running at normal oil pressure, signal should indicate open (high voltage or open circuit depending on design).
- With key ON engine OFF, reference pull-up voltage (if present) typically ~5 V or battery depending on circuit — verify with wiring diagram.
Diagnostic algorithm
- Retrieve freeze-frame and related codes. Note engine RPM, coolant/oil temp and vehicle conditions when the code set.
- Verify oil level and fill to the correct level if low. Clear code and test drive; if code returns, continue.
- Perform a visual inspection of the oil pressure switch, harness and connectors. Repair any obvious damage or corrosion and retest.
- Backprobe the oil pressure switch connector with a DVOM/oscilloscope. With ignition ON (engine OFF) record the signal, then while cranking and at idle/run. Compare to expected behavior (signal open at normal pressure).
- Measure resistance/continuity between the switch terminal and PCM input pin with ignition OFF. Repair any open circuits or shorts to power/ground.
- If wiring and connectors are good, bench-test or substitute the oil pressure switch. Replace the switch if it fails continuity/voltage tests.
- If the switch tests good but PCM still sees an out-of-range signal, connect a calibrated mechanical oil pressure gauge at the oil pressure port and measure pressure at idle and at higher rpm to confirm actual oil pressure.
- If mechanical pressure is low, diagnose oil pump, relief valve, oil passages, or internal engine wear as required. If mechanical pressure is normal but PCM still sees incorrect signal, inspect for PCM wiring faults or consider PCM diagnosis/repair.
- After repair, clear codes and perform a road test under the same conditions that previously set the code. Confirm code does not return and that oil pressure readings are within specification.
Likely causes
- Corroded/loose connector at oil pressure switch
- Failed oil pressure switch
- Open or shorted harness between switch and PCM
- Low oil level or oil pressure below switch threshold
- Faulty PCM (less common)
Fault status
Status
PCM detected abnormal signal from the engine oil pressure switch circuit (open/short/intermittent/out-of-range). Investigate oil level/pressure, sensor and wiring. May illuminate MIL and store additional oil pressure-related codes.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email