My 06' Honda Pilot's MIL is on and I have retrieved the code P0420, which is for the Catalyst efficiency below threshold for Bank 1, the rear WU-cat. At first it was intermittent, the MIL would go off after a couple of days. Then it would come back on. Then it was off for several months even though the P0420 code was stored. I recently cleared the code and got all the monitors to run. This again, caused the P0420 fault to come back with the MIL turned on. There is also a mode 06 TID of $20 and PID $7F value 0 with a Fail result that I can't seem to find any information on. I want to be sure that if I replace the rear (Bank 1) WU-TWC that I fix the problem, or could it be a malfunctioning HO2 sensor? Any help would be appreciated. I don't want to spend $300-$400 for a converter that I don't need. Also, the vehicle has about 137,000 miles on it.

 

P0420 usually means a bad cat. You can change the sensor but, chances are the cat is bad. Easy way to test the cat is to LIGHTLY tap the cat and if you hear stuff rattling around then replace it. It's recommended that you replace the sensor(s) when you replace the cat.

 

Thanks, I was hoping it wasn't the cat. but, kind of figured it was. I knew about the tapping to see if it rattled but, the rear cat. is impossible to get at with a mallet. I tried to test with an infrared thermometer but it was not conclusive. I will try a large dowel or stick to reach cat. and tap that perhaps.
Anyway, thanks again for the input. I already have the cat. replacement procedures, just need to get the money for the parts.