Code Definition

P1187 — Engine Oil Pressure Sensor circuit low voltage,

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: GM

About P1187

P1187 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1187 is stored, the module has detected a signal or supply voltage lower than the expected operating range; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1187 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The engine oil pressure sensor is a three wire piezoresistive sensor fed a 5V reference and a low reference (sensor ground) by the Engine Control Module (ECM), and it returns a signal voltage that rises in proportion to oil gallery pressure, typically sitting near 0.5V with the engine stopped and climbing well above 1.5V once oil pressure builds. The ECM uses this value to drive the oil pressure gauge and warning lamp, and on many engines it also gates the operation of variable valve timing and cylinder deactivation, which rely on adequate gallery pressure to function. DTC P1187 is set when th...

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