Originally Posted by Ep1dem1c
Check engine light on for o2 sensor only
I know that needs replaced
I will check on reverse
I was thinking either torque converter or sensor for torque converter possibly
So just to confirm, you've re-scanned the codes after it starting doing this, and there is still only the O2 sensor code.
It could be those things you mentioned. If you don't have any transmission related codes, your best bet is probably going to be to take it to a good mechanic.