Go to bimmerfest E39 (5-series sedan) section and search "low oil pressure red light", and you will see this is not an uncommon problem in the M52, M54 engines.

Possible causes:

- Oil P switch (rarely the problem), but for $10, replace it.

- Wiring issues

- Bad Vanos seals, allowing oil to leak past the seals (only at idle)

- Gunk (from extended oil change intervals) causing blockage of the oil P switch. Some people remove the oil P switch, crank for 2-3 sec to expel some oil/gunk, then re-install the oil P switch. If you do this, place a rag around the port to absorb the oil!

- Oil Filter Plastic Cap: check to be sure the tip and the 2 tiny O-rings are still there.

Most of the time, this has no significant consequence, a little "red light at idle" and that is all, but it causes nervous breakdown for the owner lol...

And of course, check your oil level first!

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT