My oil pressure gauge on my 2004 Buick Ranier with the V-8 motor shows normal pressure and then reads low pressure. At the low pressure reading all of the other low oil pressure warnings come on.
The engine oil level is fine and the engine does not make any noise as is common with low oil pressure.
Have you checked your oil level and have you changed the oil and filter recently? You don't say how many miles are on the car but the miles are really high it could be wear. If every thing else is good I would replace the oil pressure sender and see if that fixes things.
Most likely a faulty sending unit.....have it checked with a manual gage before just putting in a new unit.
Search Buick Rainier Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Buick Rainier Experts