Your cars have OBD II diagnostics onboard. If you can retrieve the codes with a scanner(for the DIY) the code (if any) will zero in on the bad sensor and tell you this.
I have two Mercedes and fortunately I have not experienced this problem. But with my Jeep Grand Cherokee, the check engine light came on. Using a code reader I got online, I read code #P0158. checking the manual that came with the scanner, P0158 refers to 02 sensor bank 2 sensor 2. Then using the shop manual I have on CD for the Jeep I looked at a schematic of the emmissions control of this vehicle. The schematic confirmed Bank 1 is the driverside. Sensor 1 is above and sensor 2 is below. Bank 2 is the passenger side with sensor 1 above and sensor 2 below.

Granted you said different makes may have different setups. But most important is getting the code. Maybe then someone on this forum can explain the meaning of the code you retrieve and direct you to the correct sensor. Good luck.

__________________


Selling used Mercedes parts on Ebay...always changing...
cdplayer51 take a look!
____________