ONLY on California version cars!
MB made the O2 sensor replacement part of EVERY 60K servce in Calif.

Just remove the O2 sensor relay as most likely it is defective,

As far as blink codes go.....code 5 is for a O2 sensor that doesn't control the mixture

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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)
Retired Moderator