I had a P0150 and P0153 code on my 2000 E320. I replaced the O2 sensor on the passenger side. The check engine light is now OFF. However, there is foul smell (like unburned fuel) every time I start the car. The mileage indicator says 7 mpg. This low mpg varies from 4 to 15 mpg on short trips (maybe within 7 miles of driving). Most of my driving is within 7 miles.

I drove over 40 miles one day, and the mpg went up to about 26 mpg. What's going on? Anybody please.

Bolero

 

you drive on?
Those codes indicate bank 2 sensor failure so looking out from the drivers seat no matter which side your steering wheel is on bank 2 is on the left side.
So if you are in the U.S. you replaced the wrong o2 sensor.