My check engine light is on, code P0240. My brother believes it is the 02 sensor. (bank 1 as the code reads) So... where is this sensor? I can't find anything online for a 2009 grand caravan.

 

Double check that code, I don't find a P0240 code listed for these vans.

As for the location of the O2 sensors, there is a catalytic convertor bolted to each exhaust manifold, the sensors at the top of the convertors are the upstream sensors, the sensors in the middle of the converters are the downstream sensors.

The sensors are as follows:
Bank 1, Sensor 1 is the Rear upstream oxygen sensor (#1 in image below).
Bank 1, Sensor 2 is the Rear downstream oxygen sensor (#4 in image below).
Bank 2, Sensor 1 is the Front upstream oxygen sensor (#3 in image below).
Bank 2, Sensor 2 is the Front downstream oxygen sensor is (#2 in image below).