P040 code

Good evening.

Can you please verify the code? You are missing a number at the end.

Roy

Sorry about that, P0420, bank 1 low efficiency.

Okay, thanks.

You need a catalytic converter. There is no issue with the O2 sensors at all. The fact that the rear O2 voltage is reading the same as the front is the reason the code set. The rear should be steady and not going up and down like the front.

The precious metals are worn out internally and the catalytic converter needs to be replaced.

Roy

CIRCUIT DESCRIPTION
The ECM observes the wave form of the heated oxygen sensor located behind the catalyst to determine whether the catalyst is performance has deteriorated. If the catalyst is functioning normally, the wave form of the heated oxygen sensor located behind the catalyst switches back and forth between rich and lean much more slowly. When the wave form of the heated oxygen sensor located behind the catalyst alternates flatteringly between rich and lean, it indicates that catalyst performance has deteriorated.

Thanks, I was hoping it was not that. One more question. With the old 02 sensors I went many weeks since the first P0420 code and never came back on. As soon as I put two new Denso O2’s in it started to show the code every day. Is that common? Are the new sensors just more sensitive or accurate in measuring the imbalance?

The new ones are just more sensitive.

It sounds like you cleared the code, the light went out and did not come back on until the PCM tested the converter and it failed its internal test three times in a row.

Clearing a code does nothing. The issue has to be addressed.

Roy

Thank you. : (

You are welcome. Keep us updated and do not be afraid to come back with more questions.

Roy

I would gladly update on how it goes, but I think it will be awhile since I do not have emissions test for awhile and I will just run it until then. Thanks again.

You are welcome.