I have bank 1 catalyst low efficiency code on chevy aveo. Is that referring to the cat right off the manifold or under the car?

Yes, but you just may have to replace the oxygen sensor, not the catalytic. There other causes associated with code P0420: Exhaust tube Intake air leaks. Fuel injectors may be faulty. Fuel injector leaks. Spark plugs may be faulty. Improper ignition timing. Again, before you start changing parts that may be perfectly good, replace the o2 sensor located in front or behind the catalytic converter.

Ok thank you Jorge. How can you check the sensors to tell which one could be bad if any? We just had the timing adjusted by the dealership to clear other codes.

If the code is P0420, it is most likely the downstream sensor (catalytic converter) however, you may want to replace the upstream sensor as well, located in the exhaust manifold; both are the same type.

Trunk cover for the interior for 2011 Chev Aveo5