Downstream O2 sensor rich

[SmokeEater2]

2000 Tahoe 5.3L

My downstream O2 sensors on both banks are running rich. On average they're showing:

Bank 1 sensor 1 = .40 v
Bank 2 sensor 1 = .44 v

Bank 1 sensor 2 = .78 v
Bank 2 sensor 2 = .73 V

Is it normal for the sensors after the cat to run more rich than the front sensors? It seems it should be the opposite.

Any ideas for what could be causing this?

I have a ping condition and I'm thinking the ECM is leaning out the A/F mix due to the rich condition reported by downstream sensors.

 

[Rivieraracing]

Try swapping both downstream O2's side to side and see if the readings/problem follows!!

 

[iwaslowr]

I am no expert in this area but are those readings abnormal for the front vs. rear sensors? If they are it sounds like the cats may need to be replaced, and possibly the sensors as well. How many miles are on the odometer?

 

[SmokeEater2]

There's 58K miles on it. From what I've been reading, these sensors fail to the rich side. I think I'm going to replace one to see if the readings from Bank 1 to Bank 2 vary. If it does, then I'll replace the other.

Anyone have a strong opinion on o2 sensor manufacturers or are they all the same, e.g. Bosch, Delphi, AC Delco, etc..