Jakob Says: My 2002 Toyota Corolla Has A P0420 And The Exhaust Sounds Loud.

  • Question for ya….have a 2001 Toyota Corolla…and it’s very loud. Sounds like an exhaust leak! Now..I went with the car to a car mechanic in town awhile back when the car was not loud due to a check engine light! Now I cant remember what the code was but they replaced the catalytic converter. I had the option of¬†stock Toyota or after market. I went with the cheaper aftermarket($400). When we got it back….it sounded like it had an exhaust leak but mechanic…said it was just the aftermarket catalytic converter that is louder. Are aftermarket catalytic converters louder. Also I’ve been occasionally getting a code which from what I read could be related to exhaust leak (Code is P0420 Catalyst System Efficiency Below Threshold).


  • Okay first thing these cars are notorious for exhaust leaks where the front pipe meets the catalytic converter. There is a doughnut gasket that fails. Most times you will notice the exhaust noise will get louder as you accelerate ¬†and the engine twists or moves slightly within the motor mounts. Always use OEM replacement doughnut gasket,springs and bolts. Check your system for leaks with a tennis ball. Did you see my post on how to do that? An exhaust leak can cause a P0420 code especially before the catalyst. Secondly you should know that 02 sensors become lazy around 90 k miles and should be replaced along with the new cat. Always use OEM replacement 02 sensors. Thirdly you should not have an issue with an aftermarket catalytic converter if it is OBD 2 compliant. I have seen cats that were not OBD compliant installed and it had everyone chasing their tails trying to figure out what was going on. I have seen cheaper aftermarket mufflers make a car sound louder due to insufficient baffling,but not an aftermarket catalytic converter. Start by checking for an exhaust leak with the tennis ball trick. Always check for exhaust leaks first with a po420 cat code. I hope this info helps you.


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