Warm up the car, the oil temperature should be at least +80°C. This temperature is reached under normal operating conditions after you have driven 10 km.
Remove the hydraulic switch. In a four-cylinder petrol engine (see fig.) it is located next to the oil filter near the drive shaft bracket "1", in a diesel engine such a switch is located on the side of the cylinder head next to the fuel filter.
Instead of the hydraulic switch, screw in a suitable pressure gauge with a suitable flange.
Start the engine, the engine should rotate at the specified speed, read the oil pressure.
Unscrew the pressure gauge.
Lubricate two or three threads of the hydraulic switch with a sealing compound, such as Loctite 242, screw it in and tighten it to a torque of 20 Nm.
Oil pressure chart
If the oil pressure does not correspond to the specified value, see the table "Diagnosing faults in the oil circulation system".