I got a po137 code from a diagnosis. It is the secondary o2 sensor having too low of voltage for normal operations. (sorry for the long story, I just want to put as much info as possible.)
I replaced with a universal Denso o2 sensor. I made 100% sure that the wires were spliced correctly according to the instructions the sensor came with. After installing the new sensor, I disconnected both battery terminals for about 10 minutes. A day later the cel popped up again! I'm guessing there is a loose wire somewhere?

 

that was short;
a day later - were you driving it in that time ??
need to get the code; may be something different that showed up

 

Splicing o2 sensor wires is usually really iffy.....why did you need to splice/cut them? Usually with the new sensor its just plug and play (at the harness in the engine bay)

 

those universal ones are cheaper but just have one (or two) bare wires on the end