For the past several months I have periodically been getting the following fault code along with check engine light on an 2007 V6.

Engine Petrol
P0420-00 - Catalyst system efficiency below threshold (bank 1) (E8)

I can clear it and it will stay away for a while. Ex first came in December and cleared. Returned in March, cleared, and again yesterday. Granted there were periods of limited vehicle use between it reappearing.

No other associated faults at this time. Only thing I have seen from the same system is the below code back in August but it never came back after clearing and was a different bank anyway.

Engine Petrol
P0157-00 (E8) Heated exhaust gas oxygen sensor - circuit low voltage (bank 2, sensor 2)

Understand the P0420 doesn't necessarily mean an issue with the cat. What are the first items I should be looking at? Exhaust leak and downstream O2 sensor? I do have a GAP took so are there any particular live values I should check out?

I was looking at the O2 sensor location diagram in the workshop manual and noticed that the location of the downstream sensors it has is different than mine. It shows them located after the cat which I would have expected.



When I look under the vehicle, I see the upstream O2 in the expected location but the downstream seems to be in the upper half of the cat. Can someone confirm this is correct? No bung or attachment point after the cat.

 

First, I would put a bottle of Mr. Gasket Cat cleaner in it. Most likely the blend of gasoline you get in your area is burning clean and there is not much for the cat to do, especially if you tend to do a lot of stop and go traffic. So, a quick clean may be enough to get some reaction form the cleaner metal.

You may indeed have a bad O2 sensor. That would be the next step. The cats are usually good for 80,000 and beyond (but there is a limit) so I would look at them last.

Hope this helps

Jeff

 

Have planned to change out the downstream O2s next week and sparkplugs as I am not sure they have ever been done. CEL has went out on its own though and not yet come back. May just be a case of too clean of fuel.

 

How did all this turn out? I'm having the same cat code 🐈

 

Both downstream O2s were change out around June 2023. I received the P0420-00 code again in April of this year. Different garage looked at it and determined one of the replaced O2s were faulty so change that one out again. Haven't seen a return since.