2001 BMW 330ci Engine won't fire

The car was idling and suddenly spluttered and died, it then would not start again. The car has fuel and the fuel pump is working and sending fuel to the cylinders. I have scanned the car for fault codes and retrieved codes 191 O2 sensor after CAT heating and 123 Electronic thermostat control. I believe the second fault code to be the troublesome one and am looking for conformation over whether this would stop the car from starting and if yes, where it is located on the engine.

Thanks