Cat oxygen storage test

Not vehicle specific, so I thought this would be the appropriate section.

How much will a cracked manifold affect an oxygen storage test on a cat? I'm guessing enough to not be an accurate enough test.

I was just looking back over at Paul's video on the Reserve Oxygen Test this morning

Thinking it out from basics the extra air into the exhaust will make it harder to get a pass result but a pass will still indicate a good cat.

The one I'm worked on last week had a cat code and I did the oxygen storage test just because and it failed miserably. Waiting on the customer to decide what they want to do.

Personally I have yet to encounter a P0420 that wasn't a bad cat but I know it is possible.
I really like the oxygen storage test and do it on any higher mileage vehicle at major services using fluttering throttle to drive the exhaust gas rich, If that makes me suspect a problem I retest using brake cleaner sprayed on to a rag.

The instructor for the training class I attended last week showed us a case study on a p0420, he used mode 6 to see that the cat had barely failed and that the O2 sensor was barely passing. Replaced the O2 and the cat still had life left in it. Cat code didn't come back.

bruce.oliver wrote: The instructor for the training class I attended last week showed us a case study on a p0420, he used mode 6 to see that the cat had barely failed and that the O2 sensor was barely passing. Replaced the O2 and the cat still had life left in it. Cat code didn't come back.

I'd be interested to hear more about this. I'm not brilliant at using O2 sensor Mode $06 data.