1985 vw cabriolet dash light OXS what does it mean when red?

It is a factory sensor that reminds you to get your maintenance tune-ups. Generally it goes off about every 15,000 miles, and when it happens people are forced to take it into the shop (they assumed dealer) and there they would tell you about all the wonderful things you need to replace and repair, or they would turn it off and send you home after a quick exam. Depending on how you feel about it you yourself can turn it off. There is a little black box the size of about two decks of cards and on the broadside of it a little white button. Hold that down for a little while, 10-30 secs, and it should go off. If you are concerned deeply about your 23yr old cars performance- take it into your local dealer or VW mechanic and they will, should, turn it off and check out your car. Good luck. When the OXS (aka oxygen sensor) light comes on, it means 30,000 miles have passed since the last OXS counter box reset (when the oxygen sensor was last replaced, or should have been replaced). The one-wire oxygen sensors on 1980-1987 Cabriolets should be replaced every 30,000 miles; the light on the dash is your reminder to do so.