99' Elantra Check Engine Light "code P1128
 

On the way home from work my check engine light came on so I stopped
at Auto Zone and the manager put the code reader on my car and it said
"p1128 Manufactures controlled air metering" this was all it said so
the manager took the code inside to his computer and entered it and it
said "upstream heated 02 sensors swapped"
Does anyone know what these could mean or what has gone bad?

Thanks