Oil Pressure Sensor

Many cars use a simple pressure switch that closes below a set pressure and lights the warning lamp. Others use a sensor that reports actual pressure to the control unit, which may also control a variable oil pump. A leaking sensor is a common source of oil leaks, and a faulty one can light the warning lamp even when pressure is fine.

Older cars use a simple switch that turns on the warning light below a fixed pressure; newer cars often use a sensor that reports an actual value. Some modern engines use the oil pressure signal not only for the warning light but also to control a variable oil pump or piston cooling jets. A faulty sensor on such engines can therefore change how oil pressure is regulated, not just what the dashboard shows.

A diaphragm moves with oil pressure and either opens a contact or changes a signal voltage. The sensor is screwed into an oil gallery on the engine block or oil filter housing, and leaking seals around it are a common source of oil drips.

If the light comes on, assume real low pressure until proven otherwise: stop and check the oil. A workshop can confirm with a mechanical gauge whether the sensor or the engine is at fault. A faulty switch can turn on the warning light even when pressure is fine, but never assume this: check the oil level and have the pressure measured with a gauge.