P0420 Code Catalytic efficiency

[washind]

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.

[danielsatur]

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.

[washind]

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.

[danielsatur]

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

[washind]

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

[maxwedge]

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.