I recently had the engine MIL go on on my Mercedes C-Class S205 while driving so I purchased an OBDII bluetooth scanner to figure out what is going on. The code I got was:
P2243(92) - Heated oxygen sensor (HO2S) 1, bank 1, reference voltage - open circuit
I read that this is usually accompanied by an engine running poorly. Since this wasn't the case I thought it could be a temporary fault and in fact a day later the MIL light went off on its own (I didn't clear the code). Unfortunately the MIL came on again a day after, and this time there were two additional codes apart from the original P2243:
P2251(01) - Heated oxygen sensor (HO2S) 1, bank 1, negative current control - open circuit P0135(01) - Heated oxygen sensor (HO2S) 1, bank 1, heater control - circuit malfunction
Again, the MIL cleared on its own after another day or so and it has been off for the past 3 days. I did some research about the expected live data from the oxygen sensors and proceeded to read the live data on the vehicle.
At idle I'm getting a constant Wide Range Equivalence Ratio (WRER) of 2.0 and this spikes very shortly down up to a minimum of 1.0 when I press the throttle. The spikes are of the order of half a second and there isn't the reverse response you would expect until the reading stabilises (first two images attached).
I checked on my wife's B-Class W246 to compare and the live data was much more as expected (last two images attached).
My car is driving pretty much normally. Sometimes there is a very short (half second) hesitance when accelerating while you're already at speed, but not sure if this is normal.
Is the Oxygen sensor faulty? Should I have it replaced?