I have a 91, have had a bunch of others. First, what is a 'volvo seiman' amm, is that a rebuilt? If you know, that is. Maybe find out as much as possible from the PO. Did you get service records?
If you have a Bosch system, the correct part # ends in xxxxxxxxx016. Maybe you can get one at a boneyard to try, but that can be shooting in the dark. I have bought many there though with only one failure. Should it come to that I have some extras. But you need to know which system you have, Bosch or Regina.
The symptom can indicate bad AMM; run the codes and see what that tells you. Read the FAQ, top right corner of page, dropdown menu. Write down details you notice and codes and come back here for more.
Oh, and this is certainly Not a stupid question! It's a normal sort of thing, with more than one possibility.