My check engine light came on, and I noticed that the car (automatic transmission) didn't want to downshift. Just that once, shortly after the light came on. After that it shifts normally.

I read out codes:
P0296 Post catalyst fuel trim system too lean, bank 1
P0036 heated oxygen sensor heater control circuit bank 1 sensor 2
P0503 vehicle speed sensor intermittent / erratic / high

Also, while under the dash, I noticed a loose black wire with reddish / brown stripe by the fuse block, dangling and not attached to anything. I presume this was supposed to be attached to something. Interestingly, the tip of the wire is cut cleanly, and there is no copper showing, just the insulation. So maybe it is supposed to dangle, maybe for some option my car didn't come with, so didn't need a termination for the wire?

When researching the codes, two can be caused by a short, so I think this could be a/the problem.

Does anyone know what a black wire with reddish / brown stripe by the under dash fuse block is for and where it should be reattached?

Thanks in advance from a newbie.