I definitely located my ring gear sensor on the passanger side 1992 602.124 when I replaced my head gasket back in April this year. It has around about an inch diameter connector. If you change your own oil next time you have your belly pan off from under the car look up by the exhaust pipe where the transmission and engine join together. Not 100% certain if the transmission belly pan has to come off also.

The function as I understand it is 2 fold one to control the EGR vacuum system and two to control the engine idle speed. I also understand it maybe used for the tach but when ime was throwing the code the tach still was functional. Once I managed to clear the code the hi low idle speed finally worked. I run with the EGR delete so no change there.