Speaking from my experience only, and not yet knowing what my root-cause is, this annoyance has not perceptably affected the engine performance or drivability as yet. If you take the black tape over the light approach, or are able to fix "whatever it may be" yourself, you may be able to drive without added expense. However, although I have tended to all the issues myself (not many really: AC recharges, timing belt @ 112K km, brakes, upper engine stabilizer, O2 sensor, oil and lube)including reseting service lights and reading diagnostics whenever the "Lamda" (check engine) light comes on, if you are inclined to go to the dealer whenever they come on, it could be a significant expense. This forum is a great help in understanding these fantastic cars and at least minimizing the expense.

Does the current owner have any information as to the codes read when his light comes on? It may have passed testing just by reading and reseting the codes. If you do not have info as to what is the system-reported cause, it may represent some pending expense as a couple of these other threads have suggested.

I love these cars. They are solid, safe, fast, comfortable, reliable and durable. The OBD-II system just seems a little neurotic, and the light "may not" indicate anything fundamentally wrong.

Good Luck in your 850 quest!

LazyPup