If the oil pressure is low in your Audi A4 can this be caused by the exhaust?

Low oil pressure on an Audi A4 is typically caused by oil sludge in 1.8 turbocharged engines. There was a recall and extended warranty service notice issued by Audi for all 1.8T engines (can't recall what model years though).

Do not drive your car, take it immediately to the nearest Audi dealer and make sure that they check the oil pan. If your car is found to have a sludge or deposit problem, Audi will pay the cost of repair or at least a portion of it.

I found this problem on my 2002 A4 1.8T Avant, which required draining and replacement of all engine oil and upgrading the oil pickup screen, filter and oil pan to reduce future sludge. Frequent oil changes would be advisable if your car is found to have this problem.