For a low pressure condition the first place you should check is the dipstick. If you find that you have low oil levels then your engine can be either burning or leaking oil. A temporary remedy can be gained by adding oil but the problem will continue until you get proper auto repairs to fix the problem. For leaking oil problems you can get new gaskets or seal so the leak will stop. For an engine that is burning oil a wet compression test and/or a leak down test will help determine what the exact problem is whether it be a worn valve and seals or bad engine rings and cylinders.
The pressure sending unit is the next thing you should check if you oil levels are okay. Check the warning lamp or gauge reading once you disconnect the unit. There may be a short to ground in the circuit if the warning light remains lit when it is disconnected. If the gauge reading doesn’t change then you likely have a problem with the instrumentation and not the engine itself.
Just always remember that it is important to check your engine at the first sign of noise or warning lights. Whether you do it yourself or have a professional do it, it will save you a lot of headache later on down the line. If you ignore the warning signs your engine gives you then you will likely start hearing a knocking noise which eventually ends in your engine seizing and stopping completely.