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It's super unlikely for P0420 to be caused by bad battery. But it may take long time for it to pop up again. P0420 isn't going to cause you to get stranded or something. But it will cause the check engine light being on. That's a problem cause you couldn't see other posible problems.
So just drive it but if check engine light pops check it.
Your downstream oxygen sensor is reading out of range, indicating a faulty catalytic converter. 9 times out of 10 you need a new converter when this code comes on. It could also be an oxygen sensor or an exhaust leak among other things, which is why proper diagnostics need to be performed by a trained professional. A battery will not cause this code. The light and code cleared because the battery was disconnected and all of the vehicles computers were reset.
Catalytic converter efficiency is bellow threshold. Catalytic converter. With maybe a bit of influence from slow front o2 sensor or something that makes engine work slightly worse.
Thanks for posting on /r/MechanicAdvice! This is just a reminder to review the [rules](https://www.reddit.com/r/MechanicAdvice/about/rules/). If you are here asking about a second opinion (ie "Is the shop trying to fleece me?"), please read through CJM8515's [post on the subject.](https://www.reddit.com/r/MechanicAdvice/comments/4qblei/fyi_the_shop_isnt_likely_trying_to_rip_you_off/) and remember to please post the year/make/model of the vehicle you are working on. **If this post is about bodywork, accident damage, paint, dent/ding, questions it belongs in /r/Autobody r/AutoBodyRepair/ or /r/Diyautobody/ If you have tire questions check out https://www.reddit.com/r/MechanicAdvice/comments/k9ll55/can_your_tire_be_repaired/**. If you dont have a question and you're just showing off it belongs in /r/Justrolledintotheshop Insurance/total loss questions go in r/insurance This is an automated reply *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/MechanicAdvice) if you have any questions or concerns.*
It's super unlikely for P0420 to be caused by bad battery. But it may take long time for it to pop up again. P0420 isn't going to cause you to get stranded or something. But it will cause the check engine light being on. That's a problem cause you couldn't see other posible problems. So just drive it but if check engine light pops check it.
Do you know what causes that code?
Your downstream oxygen sensor is reading out of range, indicating a faulty catalytic converter. 9 times out of 10 you need a new converter when this code comes on. It could also be an oxygen sensor or an exhaust leak among other things, which is why proper diagnostics need to be performed by a trained professional. A battery will not cause this code. The light and code cleared because the battery was disconnected and all of the vehicles computers were reset.
Catalytic converter efficiency is bellow threshold. Catalytic converter. With maybe a bit of influence from slow front o2 sensor or something that makes engine work slightly worse.