Disconnect the electrical wire from the oil pressure switch "1" and unscrew the oil pressure switch.
Screw the appropriate pressure gauge into the hole of the oil pressure switch.
Start the engine and let it idle. The oil pressure should be at least 4-6 bar (on models 316i produced since September 1988 and 318i produced since September 1987 not less than 4.0-4.3 bar).
Screw in the pressure switch with a new ring and tighten to a torque of 35 Nm.
In case of deviations from the specified value, see the table for diagnosing faults in the lubrication system.
Information obtained from this online resource BMWMAN.RU