# CO2 reading too high
**URL:** https://forums.speedlife.net/t/co2-reading-too-high/101343
**Category:** SON240sx Automotive
**Created:** [November 2, 2006, 1:15pm UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343 "2006-11-02T13:15:10Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@lexi777](https://forums.speedlife.net/u/lexi777)
#### Post date: [November 2, 2006, 1:15pm UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343/1 "2006-11-02T13:15:10Z")
My car failed the emissions test - the CO2 reading was too high. Is that usually something major to fix? A friend said it may be the oxygen sensor, whatever that is…
I will likely sell the car but I’m not sure whether to get that sorted out first or if people are likely to buy it as is.
It’s a 89 240sx coupe.
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### Author:  [@G-E](https://forums.speedlife.net/u/G-E)
#### Post date: [November 2, 2006, 2:00pm UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343/2 "2006-11-02T14:00:00Z")
you mean CO not CO2… check your egr operation, check your base timing too
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### Author:  [@smurf6x6](https://forums.speedlife.net/u/smurf6x6)
#### Post date: [November 3, 2006, 4:44am UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343/3 "2006-11-03T04:44:30Z")
Egr affects NOx. Base timing also mainly affects NOx but can affect hc and co due to scavenging. If you don’t know what a O2 sensor is or what it does, you should honestly just bring the car to a shop.
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### Author:  [@Flip240](https://forums.speedlife.net/u/Flip240)
#### Post date: [November 3, 2006, 8:30pm UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343/4 "2006-11-03T20:30:45Z")
check for pre o2 exhaust leaks! ECT sensor also could be a possiblity!
If its steady around 1.0 to 2.0 CO, could be cat!
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### Author:  [@lexi777](https://forums.speedlife.net/u/lexi777)
#### Post date: [November 5, 2006, 9:46am UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343/5 "2006-11-05T09:46:49Z")
Thanks all for your responses. I probably didn’t make myself clear. I wouldn’t know an egr etc. if it bit me in the umm… ankle so I definitely wasn’t going to try and fix it myself. :oops:
Really I was just trying to ascertain whether a high CO reading necessarily meant a major repair (say over $500). If that’s the case I might just try and sell the car as is if possible, to save myself the hassle of getting it to the shop etc.
Anyways, thanks again.
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### Author:  [@G-E](https://forums.speedlife.net/u/G-E)
#### Post date: [November 5, 2006, 1:14pm UTC](https://forums.speedlife.net/t/co2-reading-too-high/101343/6 "2006-11-05T13:14:13Z")
most emissions problems aside from a bad cat are cheap to fix \<$100
if you post all your percentages we can tell you whats wrong for sure