P2201 code n a gasoline engine?
 

I've got a 2014 E350 with the M276 gas engine.
This morning the CEL came on, I checked it and it says code P2201 which refers to NOx sensor.

"P2201 is a diagnostic trouble code (DTC) for "NOx Sensor Circuit Range/Performance Bank 1"

I believe only diesel engines have this sensor, am I correct?
It has happened once about 2-3 months ago, I just cleared it.
After filling up this morning it came back.
I usually overfill the gas tank, could that have anything to do with it?

I believe it's referring to the upstream O2 sensor readings on Bank 1 side, even though it's calling it a NOx sensor. NOx sensors are typically wideband sensors, so you interpret the voltage data a bit differently than you would for a narrow band O2 sensor.
Someone else will hopefully verify this info.

Thanks Mud. It seems to be intermittent, it hasn't come back yet so I'll just wait and see while I dig up more information about it.

IMO your best bet is to simply look at real time scan data, you don't need specific MB scan software to at least give you an idea of what's going on.

A decent OBD2 scantool that can show OBD modes 1-4 can provide real time and freeze frame data. Real time shows what the basics are doing as the engine is running, such as timing, fuel trim, O2, TPS, etc. Freeze frame is a snapshot of what the data was at the time the fault code was triggered. That can help see where something was out of range.

As you look at the run data, you can see what the O2 sensor voltage is doing, and if it's causing the ECM to command lean or rich long term fuel trim. Short term fuel trim cycles constantly between lean to rich or 0 to 10% range but it does not set a code if it's out of range. If the STFT parameters lean more rich or lean then the long term fuel trim strategy changes to reflect the ECM working to control the mix. If LTFT can't control the mix then a code is set. LTFT can tell you if the ECM is having an issue controlling a vacuum leak for example if it's skewed to a high positive percentage (constantly adding fuel). I'm telling you all this because they rely initially on O2 sensor input.

An O2 sensor malfunction can cause the ECM to go very lean or rich trying to keep the mix correct. That malfunction can be on the wiring side as well, bad connector, etc but most folks usually see the code and put in another sensor. More often than not that's a fix but not really a good diagnosis just putting a part in. I always replace O2 sensors with oem parts to avoid any calibration issues with what the ECM wants to see. So take a look at what your O2 / NOx sensors are doing.

Thanks. I've got a Bluetooth OBDII adapter and CarScanner app on my tablet, I'll see what I can find.