P138600 Error code

Got this error code…,Read that it could be one of the following. low voltage, Loose connector and and a faulty Rear O2 Sensor. The car hicupps once then follows through fine. Before getting an O2 sensor where else can I look…Got a new battery, and connectors are all tight.
Can anyone share any insights on the matter…Would appreciate any inputs.

Thxs Much.,