I was caught up in the Tesco fiasco and had the oxygen sensor changed. However, the engine management light has come on again with the message on the AA mans fault diagnostic equipment as 'Oxygen Sensor CO2 Bank 1'.
Could anyone tell me if this is the sensor nearest the engine or the other one? I have already had this one changed and I don't want to pay again for the same job or could it be something else?

Any help would be great.