O2 reading relationship and cat function

[Protec]

Having a strange issue that I hope someone can educate me about.

LS Series L9H w/ E38

Noticed Bank 2 Sensor 2 only switching 50-100 mv , while Bank 1 Sensor 2 would follow B1S1 and have full swing in mv.

I swapped in a new sensor and it did not change the results.

My question is what does the downstream 02 mv swing look like in a normal functioning cat? Would it follow the upstream sensor in its reading or would that mean that no catalyst action is taking place?



Numerical Representation:

B1S1 = full swing 75-900mv
B1S2 = Follows S1

B2S1 = Full swing 75-900mv
B2S2 = Only changing 50-100mv staying in the 600-750mv range



Thanks in advance,


John

[joecar]

If the downstream cat follows the upstream, then the cat is not working.

[joecar]

See attached image...

HO2S12 shows B1 cat has failed

HO2S22 shows B2 cat is ok

[Protec]

Joe,

Thanks and that's what I thought.

I lost the Bank 1 side coil packs due to a harness issue and had to drive it a mile to a parking lot. Looks like the fuel dump onto a hot cat did it in. Amazing that the rear sensor still worked as it melted the cage and part of the sensor. Time for new cats and O2's


Thanks for sharing the information and screen shot.


Regards,

John