P0420 Code Catalytic efficiency

:smile: Problem solved!

After having changed my manifold, front O2 sensor and Catalytic Converter two years ago, I have been chasing a P-0420 code ever since (Cat efficiency). First I changed the front O2 which gave some limited relief. Next I changed the rear O2 which didn't help at all (but I likely needed it anyway). Then I read in this forum where there is supposed to be a 10-15% temperature increase from the front to the rear of the Cat - mine was the same. So, I changed the Cat again; problem solved! I'm also pleased to report that the garage covered the cost of the Cat under warranty.

Thanks Automotive Forums.

Thanks for the feedback, the down stream H02 sensor, or 2nd sensor is what gives the signal to the ECU/PCU that your catalytic converter was bad.

Using a good OBD II scanner can check temps on catalytic converters too!
Did you use a hand held infrared temp gun?

The bad, or blown cat will run cooler, throw a DTC, and sound like a empty tin can.
A plugged catalytic converter can get hotter, and wont throw a DTC.

Caution - Make sure you remove all broken pieces of cat down stream of exhaust to the tail pipe.

Thanks for the prompt feedback.

I'm new to OBD readers and didn't know I could read the temps (obviously neither did my mechanic). I used a cheap hand-held infared gun that did the trick. No debris was found, but now that you mention it, it did sound a little throaty but since I don't run a rear resonator it didn't register with me.

Do you know the federal warrenty on Cats is 8 year/ 80K miles?

No, I didn't know. I wonder if that applies here in Canada also.

Never saw a scanner read cat temps, I use the i/f unit, it should be about 100 degrees higher temp at the outlet than the inlet. A graphing scanner can compare the o2 sensors post and pre cat which is what the pcm does to check efficiency.