Check Engine Light On. What codes mean

So my check engine light is on. Got it checked at Autozone and this is what it said:
Oxygen sensor heater control circuit low-bank 1 sensor 1
Probable cause
Open or short circuit
poor electrical connection
failed oxygen sensor
EFI relay fault
Tuck is not running bad. How can I fix this myself? Any help greatly appreciated

 

The heater circuit for the air/fuel sensor is not working correctly. It is the front sensor. The one in front of the cat. This circuit helps the sensor warm up quickly after a cold start. When I got that code (P0031), I replaced the sensor with a Denso from Rockauto. Make sure you use OEM for your year, not a generic. Can also get the discount at Rockauto for TW.

I have replaced one on an 04 automatic and an 03 manual. The automatic is easy and the electrical connection on the manual is hard to get to. Make sure you soak the two nuts down with penetrating oil for a couple of days before attempting to remove it. Should make it easier to get out.

 

Thank you so much. Really appreciate it. Love this forum

 

Dumb question. Where is the upstream O2 sensor? I thought there were 2 but I only see one. The visible one is between the exhaust manifold and cat converter. I'm assuming the visible one is the downstream?

 

The upstream sensor is between the exhaust manifold and the cat. There is a downstream sensor after the cat. It tends to be more at the 1:00 position (looking from the rear axle). These two monitor what is going into the cat and coming out of the cat.

 

Geez I'm so stupid. I didn't see it from where I was under the truck. I see the downstream now. Part is ordered, should be an easy fix. Thank you