Causes of lean condition trouble codes P0171, P0174 - GM 5 3L

Causes of lean condition trouble codes P0171, P0174 - GM 5 3L

I was watching this video and had some questions regarding the B2S2 O2 diagnosis. Obviously not arguing with the diagnosis, just some things I don't understand.

Why is this a sensor problem and not a oxygen storage problem? The first thing I thought about after seeing this was the oxygen storage test on page 5-13 in the book, and how there is a 2-4 second delay in the downstream O2 response after turning on the propane. Isn't revving the engine to WOT at 32:57 basically just like adding the propane since it's forcing the AF mixture rich? Wouldn't we expect a downstream response to be delayed a few seconds, or not see one at all? Also, later on near the end 32:48 the B2S2 is oscillating between about 500-700mv. Isn't an oscillating downstream also a sign of a problem with the cat? Thanks!

Not speaking for ScannerDanner here, but I can add my thoughts. Thanks for the link, BTW. I love how the YT links work with the 'Start at' option.

I think his issue with the B2S2 wasn't so much with the timing, as the amplitude of the signal itself? Not being able to force it above 800mV, as compared to the B1S2 sensor. The signal was definitely oscillating at 32:48, but other times it was just aimlessly wandering around. :lol: Like at 29:56, with the signal floating around 300-400mV.

There definitely COULD be an oxygen storage problem with this cat, especially if the owner had been driving around with lean issues for too long. But, with the downstream code stored, the safe move would be to replace the sensor and let the cat monitor run.