Faulty engine oil pressure sensor (common failure on GM engines); Damaged or chafed wiring in the sensor circuit, especially near hot exhaust components; Corroded or loose electrical connector at the oil pressure sensor; Poor ground connection for the sensor or ECM; Low engine oil level or low oil pressure causing the sensor to read below normal range; Failed ECM driver circuit for the oil pressure sensor (less common)

DTC codes / GM codes / P1187

P1187 · GMEngine Oil Pressure Sensor Circuit Low Voltage

Q: What does code P1187 mean?

Engine Oil Pressure Sensor Circuit Low Voltage. P1187 on GM vehicles means the engine control module (ECM) has detected an abnormally low voltage signal from the engine oil pressure sensor circuit. The ECM expects a voltage within a specific calibrated range that corresponds to actual oil pressure, and a reading below the minimum threshold for a set time triggers this code.

P1187 on GM vehicles means the engine control module (ECM) has detected an abnormally low voltage signal from the engine oil pressure sensor circuit. The ECM expects a voltage within a specific calibrated range that corresponds to actual oil pressure, and a reading below the minimum threshold for a set time triggers this code.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Oil pressure warning light or message on the instrument cluster
Oil pressure gauge reading low, pegged at zero, or fluctuating erratically
Check Engine Light illuminated
Engine may enter reduced power mode or fail-safe operation on some GM models
Often no drivability symptoms besides the warning lights
In rare cases, a chime or warning message about low oil pressure

Common causes, most likely first

Faulty engine oil pressure sensor (common failure on GM engines)
Damaged or chafed wiring in the sensor circuit, especially near hot exhaust components
Corroded or loose electrical connector at the oil pressure sensor
Poor ground connection for the sensor or ECM
Low engine oil level or low oil pressure causing the sensor to read below normal range
Failed ECM driver circuit for the oil pressure sensor (less common)

How to diagnose and fix it

Check engine oil level and condition; top off or change oil if needed
Inspect the oil pressure sensor connector and wiring for damage, corrosion, or looseness
Use a scan tool to read live oil pressure sensor voltage and compare to mechanical gauge reading
Test the sensor circuit with a multimeter for reference voltage, ground continuity, and signal voltage
Replace the oil pressure sensor if voltage signal is incorrect and wiring is good
Verify oil pressure with a mechanical gauge to rule out actual low oil pressure
Clear codes and test-drive to confirm repair

What GM techs check before replacing the sensor

A low oil level or worn oil pump can set P1187 even when the sensor is working perfectly, so always verify actual oil pressure with a mechanical gauge.
The oil pressure sensor on many GM engines is located behind the intake manifold or near the oil filter housing, where heat and oil leaks commonly damage the connector and wiring.
Corrosion inside the sensor connector pins is a frequent cause that a visual inspection alone may miss; gently wiggle the harness while watching live data on a scan tool.
Some GM vehicles use the oil pressure sensor signal for variable valve timing or cylinder deactivation, so a faulty signal can cause driveability issues beyond a simple warning light.
After replacing the sensor, the ECM may need a relearn or calibration procedure on certain models; check service information for the specific vehicle.

Can I keep driving with P1187?

If the oil pressure warning light is on and the gauge reads zero, stop driving immediately and check the oil level; continuing to drive with actual low oil pressure can destroy the engine. If the gauge shows normal pressure and only the Check Engine Light is on, you may drive cautiously to a repair shop, but avoid heavy loads and high speeds until diagnosed.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.