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.