Gentlemen, Most grateful for any ideas on the following.

I have an Audi A6 2.5 TDi 2002. The red animated 'oil can' low oil pressure warning light icon displays for several minutes about once a month and then resets. This happens when the car is warm, cold, fast or slow road speed or revs, although I have the impression that it happens when on a steep incline or when accelerating hard. Car is now at 100,000 miles but this fault has been there since 20,000 although it now happens more frequently. Audi main dealer has done 5 hours of diagnostics and 'in depth' checks but can't find any problem and I've been advised to 'monitor'. Maybe they don’t believe me but it's a bit un-nerving driving at motorway speeds with this light on. A new issue is that the water temp gauge drops to minimum in one step and then returns to its usual 90°C also in one step intermittently but not necessarily at the same time as the oil warning light so this may or may not be connected to the oil light fault. V6 Engine runs smoothly, sounds as good as a diesel ever does, no oil leaks at all, oil level is always at max on the dip stick, oil changed using correct grade regularly and oil is acceptably clean on a spot test, steady oil temp on gauge when running, fuel economy is as good as ever, all fluid levels are OK and no sign or smell of anything abnormally hot, turbocharger can be heard spinning down sweetly when engine is turned off. How does the sensor transmit to the ECU is it an analogue voltage or digital signal, could something be interfering with it?