Low oil pressure switch
0.75-1.0 bar with grey colour identification

If your T25 buzzer comes on at 2k rpm this can sometimes be solved by replacing this sensor along with the high pressure switch and/or the coolant temp switch

To fit:

T4 1X, 1.9 Diesel 90-12/95
T4 ABL, 1.9 Turbo Diesel 90-08/98
T4 AAB, 2.4 Diesel 90-07/94
T25 1.9 & 2.1 Waterboxer 86-92
Mk3 Golf, TDI engines 1Z, 1Y, AAZ, AEY, AFN