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Car looses power intermittently


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Here is what has happened.

I recently bought a 1999 civic 150,000 miles, EX/ Manual. The next day the check engine light came on, fault code P0420. I was told it was either the Cat or the O2 sensor. As I was driving it I lost hp until I down shifted and re-applied the gas . I thought that it may have not had enough hp to do it since I was in 5th and going up hill. It happened again at a lower gear, so I decided that the exhaust was backing up and replaced the Cat. The Cat was bad. After the replacement it happened again, not when I was accelerating. I tried to shift (did not work, and the car misfired). The car shut down. When I tried to restarted, it started first try and drove. When I was going home, shortly after it did it again, but did not restart. I was waiting for a tow, decided to try again and it started right up. It drove perfectly. The Cat was bad and had a hole it it. The check engine light has not come in since the cat was replaced. Does anyone have any idea what could be causing this to happen? To clarify, when the car looses power the reves track with speed but when the gas peddle is depressed nothing happens (unless it is in neutral). Any suggestions will help. Thank you.

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Did you replace the sensors?


You mentioned that someone told you the catalytic converter or the oxygen sensors can cause the p0420 code. That is mostly correct. There are a veritable mountain of things that can cause it as that code isn't a failure code. It is an emissions reading outside of normal operating parameters code. The catalytic converter is sometimes the cause of the error but more often than not the sensor itself has failed. Considering that the sensor is considerably cheaper than a new catalytic converter most sane people replace that first. Keep in mind that this error code can be generated by issues other than a failed sensor or a failed converter.


Start with sensors, then start worrying.

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