Engine light OBD code P0135

[Palmeroj]

1996 GMC Suburban K2500 7.4 check engine light goes on for a few days, then off, then back on again. I put the OBD and it shows code P0135, Oxygen sensor bank 1 sensor 1. If I'm not mistaken, this is the upstream sensor on the driver's side.

 

I did a web search and came up with a lot of hits, some sensors are labeled as "heated sensor", some are not. I have a few questions.

 

1. Should these be replaced in pairs, both upstream and downstream?

2. Does anyone have a part number, or link to the correct sensors.

 

Thanks.

[riverbanks]

I would check the harness connection first, sometimes they corrode,a green fungus will be visible, everything looks fine,Just swap out the bad one,drivers side,front one,you'll get codes for the others, when,who knows