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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29396
Experience:  GM Grand Master Technician 2007. 14 years experience.
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1999 Suburban: 5.7L engine..PO..I replaced the downstream O2 sensor

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1999 Suburban 5.7L engine. I got the PO 420 Code coming back over and over so I replaced the Cat Convs. Code was cleared at the shop and came back so then I replaced the downstream O2 sensor. The code was cleared and now I have it back again? Do I go ahead and replace the upstream sensor as well?
Welcome. Did you replace the proper sensor down stream? I made the mistake once of not realizing that the exhaust crossed over in and the left rear one was for the passengers side bank. Is this something that could have happened?
Customer: replied 7 years ago.
I replaced downstream sensor that I saw. Because I only ever saw one. Now that you say it I found the other under the frame rail. Wow that was a very good question and at first I was certain that I had changed out the correct one. I went back out to the truck just now and looked and now I see the "other" sensor on the "correct" bank! I assume that would be the issue now huh?
I would think it might be. Worth a try. If you still have the old one, I would simply install it to swap with the other one.
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Customer: replied 7 years ago.
Thanks for the help. Much to my own amusement now and of course to publicly admit my own stupidity....I appreciate the support. I will let you know if this one works out. Thanks