E90 3.0d Oil pressure switch/sensor

[Vee]

Does anyone know how oil pressure is measured in the 2007 30d/35d engine and the location of the sensor ?
I'm getting an intermittent red flashing light as revs drop to idle. It goes away as soon as the accelerator is pressed.

There appears to be enough oil in the car so if easily accessible I think changing the sensor could be a start.