O2 sensor

[dp213]

I am working on a 03 Impreza TS, it has a p0031 code. The car has 94k original miles and in great shape. The code is for the upstream sensor so I unplugged it and was checking for ground. It's a 4 wire sensor, does that not ground to the chassis. The downstream sensor does.

 

Anyone know if the black wire grounds to chassis or where it does.

 

By the way, I'm checking the harness side.

 

Thanks