Hey guys, W221 here. My OBD2 whatchmacallit arrived today, which turned out to be good timing... After leaving the office and getting into my car, and turning it on, I realised I'd left something behind. So I turned the engine off and was about to get out of the car when I decided I'd just grab it tomorrow as it wasn't important. So I turned the ignition on again, but the engine wouldn't start - the ignition just kept making its noise (I have no idea what this process is called or what the noise is called, but it was a normal ignition noise... it just went on and on and wouldn't start.) So I turned the car off again, and waited a few seconds. I tried again and the car started up like normal, but this time there was a check engine light on. I drove the short distance home, during which time I paid close attention to the noise and feel of the car and noticed nothing of any concern. After getting home I plugged the OBD2 in and booted up Torque, and scanned for the error codes. It came back with the following: [RED] P0335 - Powertain Crankshaft Position Sensor A Circuit [GREY] P2045 - Powertrain Reductant Temperature Sensor Circuit High Input I have no idea if these are connected or not, maybe one was already there? I'd never checked for fault codes and nothing had come up before. The Red error is also flagged as "Current Fault". I've done a little research and can't really see much about the error, other than apparently P0335 will clear on its own after 4 or 5 ignition processes without an error. I don't think I've turned the ignition on that many times since the error was reported, though. The engine sounds normal, and the car feels normal to drive. I'm hoping I can get away to my local Merc garage tomorrow lunchtime and see what they say but I was wondering if I could get some advice first from here?