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Looking into buying a 156K 2000 civic lx of this guy cause my 98 dx was wrecked. Has a CEL for P0420, I test drove the car and i'm concerned with the transmission, during 2nd going to 3rd gear the car seems like it doesnt want to leave 2nd it over revs in 2nd gear (still picks up speed), shifts to third around 3500 to 4000 rpm. It's an auto so I'm wondering if it could be related to the engine maybe not running right due to the malfunction. Also the tach wobbles up and down. Car looks clean and very well taken car of I'd really hate to miss out on this car but I don't want to end up paying for a new tranny down the road. This is time sensitive so please all you pros lend me some support tell me what maight be going on. Thanks

 
Rep Power: 314

The problem is gear slippage in the transmission. Only buy it if your okay with replacing the transmission within a year.

 
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I thought when the transmission slips it feels like your in neutral before it slams into gear? Thats not the case here, until third gear 2nd gear is still engaged it feels like it's holding that gear to long I have to give it more gas to get it to shift and when it does shift it is smooth.

 
Rep Power: 314

Ahh ok I misunderstood the "overrevving in second gear" .. still the transmission.

 
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I told the guy that I would like to have it checked out at a shop to rule out wether it could be engine related, of course if the engine isn't running properly you can expect transmission problems. He was more than likely fine with holding the car for me until sunday. So you still say it's slipping? Beside a bad cat what else could set off a p0420 in some rare cases?

 
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I could also hear what sounded like spark knock over the engine.