I've got these two codes on my 03 disco now. I cleared them last night and drove the truck for about 8 miles. No SES light.

At the next key cycle the light came on again. I can see there is a lot of soot around the tail pipe and the exhaust smells like a rotten egg.
All four O2 sensors are about two years old and prior to reinstalling my engine, I bench tested all 4 sensors, (meaning, I heated the tips of each and verified voltage as well and continuity on the heater circuit side). I found no issues.

The pic below shows my scan gauge readings as of this morning. Is it not odd that both the upstream sensors show zero reading? Any help is greatly appreciated

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That is unusual. Get a $5 elm327 scan tool off Amazon and use the free torque app for Android - then graph your 02 output. There are three possibilities:

1. They are completely dead. They will start at zero volts cold and stay there no matter what.

2.They are not dead, but you have a different condition that causes them to seem that way at operating temperatuure. They should read near 1 volt on cold start, then start cycling. Sometimes when there are other problems they will start near one volt then go to zero volts as it heats up.

3. They are slow responding or have a limited range. If this is the case they are likely bad.

You can't see any of the above with your ultragauge, you need an analog graph.

 

Same drive this morning, At operating temp and same speed. Right bank upstream sensor still dead. Left bank has magically come back to life.

 

They don't read steady, they cycle between zero and 1. I am not familiar with you gauge, how quickly does it update? Can you see the cycling?

 

yes, the cycling is immediate when on this screen.