I have a 1994 C280 and I got the CEL on, and the code reads P0131 - O2 sensor circuit low volts (Bank 1 Sensor 1).Does anyone have any suggestions besides going ahead and changing the entire O2 sensor located before catallytic converter ?
Also I have got a yellow warning light that is just to the left of CEL which started to come on and off when I washed the car today. Anybody knows what that is ?

Thanks