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post #1 of 5 (permalink) Old 06-02-2018, 08:27 AM Thread Starter
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Knock Sensor and O2 Sensor Malfunction?

Hello everyone,
I need a little help here because I am very confused and need help picking a starting point. I have a 2008 cobalt ls, 2.2L 5 speed. I have had this car since 2008, it is my first car, she just turned 100k miles last year, and she is my baby! The last three years I have been storing her for winter, I live in NY and winters are rough on cars here. I finally got a big boy job and decided to spend a little money on the blue beauty. I bought a Magnaflow catback exhaust for her, and the install went on without a hitch. About a week after doing the install, a check engine light came on, something this car has never done to me in 10 years. I plugged in a code reader and got knock sensor circuit low, downstream o2 sensor lean, and downstream o2 sensor rich. I did what Magnaflow said and disconnected the battery after the install to reset the computer, but it is still giving me a light, and I can smell gas from the exhaust now, another thing this car has never done. My point of confusion is, did something go wrong with a sensor while it was in storage? The car is getting older and it may be a coincidence considering I've done catbacks on other vehicles before and have had no problems. Could a knock sensor cause the o2 sensor to mess up? Can the o2 sensor cause the knock sensor to malfunction? Did both sensors go bad because they are old? Did putting a catback on it cause an issue? I'm reaching out for a little help here. It runs and drives fine, no new noises (other than the exhaust, which sounds sweet!). I'm just confused, any advise would be much appreciated. Thank you for taking the time to read this!
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post #2 of 5 (permalink) Old 06-02-2018, 11:25 AM
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Did you check the EXH fuse under the hood? It supplies voltage to all 3 sensors you are pointing to.

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post #3 of 5 (permalink) Old 06-19-2018, 03:44 PM Thread Starter
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I have not checked that, I will this weekend. Another update on the situation. The check engine light now plays a fun game of I come on when I want. It will be on for a few days, then off for a few days, then on for a day, then off for a week. No regularity or pattern. If this helps at all let me know what you think, otherwise I'll check that fuse this weekend and I'll get back to you on what i found out! Thank you btw!
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post #4 of 5 (permalink) Old 06-20-2018, 06:29 AM
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Well it wouldn't be the fuse if the CEL goes on and off. Sounds like an HOČ getting old and out of range giving you intermittent pending codes. Make sure your oil levels are topped up.

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post #5 of 5 (permalink) Old 06-23-2018, 08:25 AM Thread Starter
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That what I was thinking originally. Oil is good, it's on a fresh change 400 miles ago. do you know the ohm range a sensor is supposed to be in so I can check it with a multi-meter? Is there a thread that exists that would tell me this? Thanks again!
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2.2 , 5 speed , catback exhaust , knock sensor , o2 sensor

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