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Hi,

2006 Pilot 4WD with 135K miles. During this past year the exhaust has been getting louder, just a litte rumble during acceleration. The noise doesn't seem to come from the muffler, but more from the middle of the car.

On Saturday, we got the check engine light during one short trip and later on a longer trip. On Sunday during short trips the light didn't come on. My local parts store scanned the code and got a P0420 Rear Bank catalytic converter below threshold.

Some research suggest that the P0420 code could be due to an exhaust leak (the noise I hear), or bad gas, or a bad sensor.

Does anybody know how an exhaust leak could throw this code? Could this be an cheap fix, or do I really need a new catalytic converter?

Thanks!
 

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From simple and cheap, to hard and expensive:

  1. First, check for a crack in the airflow tube after the air filter or any obvious vacuum leaks.
  2. Check for coolant loss/leaks.
  3. Throw in a bottle of Seafoam or Techtron with your next fill up (of top tier gasoline).
  4. Check for loose spark plugs and retorque to spec if needed.
  5. Clean MAP sensor.
  6. Replace both upstream and downstream Air/Fuel and O2 sensors.
  7. Replace catalytic converter.

Hey, Piloteers, jump in if you think of anything else. :)
 

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If you don't have to get emissions testing in your state just leave it alone. That's my .02.
 

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Hi,

2006 Pilot 4WD with 135K miles. During this past year the exhaust has been getting louder, just a litte rumble during acceleration. The noise doesn't seem to come from the muffler, but more from the middle of the car.
Based off the age, mileage and the exhaust getting louder take a look at your exhaust system particularly the flex pipe section before the CAT, heat shields around the CAT and the CAT. There is a resonator/muffler in the middle before the system terminates to the muffler.
 

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Does anybody know how an exhaust leak could throw this code? Could this be an cheap fix, or do I really need a new catalytic converter
If the leak is before the sensors, then the sensors aren't reading recirculated exhaust gas, they're reading O2-rich outside air - and that will definitely throw a code.

If the leak is after the sensors, it can increase air velocity past the sensor (as the gas rushes out the hole instead of out the tailpipe) - when the leak gets big enough, the exhaust gas escapes fast enough that it also typically leads to readings out of spec that trigger a code.

I would highly recommend you first identify and fix the exhaust leak before any other troubleshooting. Exhaust leaks are easy to find, simply start the car and feel for escaping air.

However, just recognize that 'rumble' you hear could be a bad catalytic converter.

Regardless, you've had the problem long enough that if you find a leak - fix it - and then inspect the O2 sensors.
 
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