Thread: P4020 - Catalyst Converter Below Efficiency Threshold (Bank 1)

So I got a P4020 code (Catalyst Converter Below Efficiency Threshold [Bank 1]). Is it safe for me to assume that "Bank 1" is the pre sensor, and not the the post?

Also, just to confirm....I want to make sure that there are only 2 oxygen sensors on my 2005 Grand Prix (Base Model).

Lil' help?

The code is suggesting your cat is bad.

Nothing about the O2 sensors.

Originally Posted by BillBoost37

And...your title is incorrect should be P0420

You're right....my bad.

Originally Posted by sic6

Make sure you don't have any exhaust leaks after the cat.
It will also throw a cat code.
Mine was leaking between the cat and rear o2 sensor.
Repaired the leak, code never came back.

Cool.

I'll give it a look-see. If I don't see any visible leaks; then I guess I'll have to end up replacing it and the O2 sensors. I know the code has nothing to do with the 02 sensors (as matt5112 pointed out) but it's probably the original ones, so...while I'm down there.