Hey guys, my friend owns a 2001 2door 4wd drive blazer, LS. His check engine light was on so, i used my code reader to pull codes. They pulled p0131, P0135, P0141, P0151, P0154, P0155. All o2 codes, so we went to pep boys and got three new o2 sensors. I installed all three, and reset the codes. The CEL was off for about two days, then it came back on. Once again i pulled the codes and it read. P0135, P0141, and P0155.(41 and 55 were also pending codes)We purchased OE bosch o2's. This is really confusing to me because, to my knowledge all three of these codes have to do with heater circuit faults. Which means the sensors came bad out of the box?
Another thing that is confusing me is that several months ago, my friend replaced the first two sensors, and left the one after the cat, stock . I have been searching this forum and read that the bosch plugs are not the "best" but what are the chances of getting so many faulty o2's in a row?
I was thinking about testing them with a meter, but that is a whole new learning process for me. And if my hypothesis is right, and the sensors are not heating up to read flow(Heated circuit fault) then the sensors are just faulty? If you guys can help me out it would be appreciated, and PLEASE correct me if any of my statements, and observations or wrong, this is my first real chevy i have worked on. Thank you.

 

If they all are heater codes, I would check the fuses, and wiring. The chances in the first place to have that many O2's go out all at once are just as rare as getting 3 bad sensors at the same time. And only use ACDelco O2 sensors!! But 3 of those codes are for low voltage, which usually means the O2 is sending low voltage back to the ECM, IE lean running, IE vacuum leak, low fuel pressure, etc. If you have that many O2 codes you need to check the other systems first. HTH Korey