I was driving down the road 3 weeks ago or so and my oil pressure gauge was all over the place.Knowing that the oil pump in these cummins engine's are a beast,SENDING UNIT FAIL! The only oil pump fail I have seen was a marine engine with a fram filter on it..

Scanned for codes and produced a PO523=Oil Pressure Sensor High

Went to the cummins dealer and picked up a new oil pressure sender part#4921511.This part number is determined by the engine code plate that is on the side(Drivers Side) of the gear case. To take the old unit out I used a 1 1/4 inch socket to remove the sender (On the driver side under the cummins ECM). For the install the new sender was a 27mm deep.

I hope this helps out and here are some pics.