When the oil pressure starts to rise, the oil pressure sensor contact in the engine is triggered. The current circuit is broken. The control lamp goes out. Cold engine oil is quite viscous. This causes high oil pressure, so the control lamp goes out already when the engine is started or after that. In hot summer, the oil in a hot running engine is very thin (low viscosity). Because of this, his pressure, accordingly, becomes lower; the indicator light goes out only at higher speeds.
The illustration shows the left front side near the cylinder head of a diesel Volkswagen: 1 - temperature sensor; 2 - oil pressure sensor; 3 - engine temperature sensor; to determine the required pre-heating time, the sensor sends a signal to the pre-heating relay.
Malfunctions
If the oil pressure warning light suddenly comes on while driving, it is dangerous for the engine.
If it lights up briefly during sudden braking or fast driving on a curved road, the oil level has obviously dropped below the minimum mark. Check the level and top up with oil if necessary.
If the light stays on for a long time, you must stop the car immediately!
Then first of all check: is there a short circuit in the blue-black wire going from the oil pressure sensor to the LED. Turn on the ignition, remove the wire from the oil pressure sensor. The indicator light should go out when the engine is off. It is best if an assistant observes this. If it continues to burn, then the wire has worn through somewhere and has a contact "to ground". This will not cause damage to the engine; you can go further.
(The original information is posted on the resource VWManual.ru)
However, the oil pressure warning light usually lights up to indicate that there is not enough pressure in the engine's lubrication points. In most cases, this is not caused by a defect in the oil pump, but most often by a sudden loss of oil. For example, a drain plug has come loose. If the malfunction poses a danger to the engine, the car should be towed.
If the oil pressure indicator light is constantly on, the cause is often a faulty sensor. But only by replacing the sensor can this be determined.
When turning the ignition key, the oil pressure light does not light. Turn on the ignition, remove the wire from the oil pressure sensor and press it to the "ground"; if the lamp now lights up, then there is a fault in the oil pressure sensor. Replace the sensor. If the lamp does not light up, then there is a fault in the power supply wire, in the lamp itself, or in the LED.
Note: If the oil pressure warning light comes on after driving through a large puddle of water, this is usually due to the following reason. The oil pump is driven by the intermediate shaft, which in turn is driven by the smooth back of the toothed belt. If the toothed belt tension is too low, it is oiled, or, for example, water has entered this drive, the toothed belt briefly slips on the intermediate shaft. As a result, too little oil is supplied. The toothed belt tension and condition must be checked immediately. See chapter "Engine".
Replacing the oil pressure sensor
The oil pressure sensor is located in an accessible location on the left side of the cylinder head (if you look in the direction of movement)
When replacing the sensor, tighten it with a new sealing ring. The torque is 25 Nm.
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