First of what model & year car?? Most of the engines with ME fuel systems will read negative O2 sensor voltage, but they will cycle to positive as well.
ALSO depending on year model universal sensors WON'T work properly. Even a 1997 E320 uses different sensors than a 1996.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)