oil pump!!!

my 16 yr old son has a 1991 Lumina Euro w/ a 3.1..His oil light and pressure guage have been acting funny. the light comes on at idle and when slow driving, the guage reads very low after its warm. Do they use different sensors? Also, if the oil pump is bad, does the pan drop easily for access? He is not very mechanical, so all fixing fall on my shoulders. Looking for some info. thanks..