Catalyst test vs Post O2 test

[flea]

Can anyone explain/clarify the difference between these two tests?

The post cat O2s are obviously to monitor catalyst efficiency.

Is the post O2 test simply to verify these O2s are being heated/and or switching properly?

Thanks

[flea]

So no one can explain the difference between and/or relationship between these two tests?

Disabling the post O2 test eliminates the low catalyst efficiency DTC. What then, is the purpose of the master catalyst enable/disable?

[Bill@HPTuners]

I'm not exactly sure of the purpose of the two tests, however I'm pretty sure both of them can basically take over your AFR at any given moment which can be a bit unnerving when your commanded afr goes to 16:1 for no obvious reason which is why the switches were added originally.

[flea]

Thanks Bill,

I appreciate your candor. I've been digging around on the site, my Helms manual, etc. and I can't quite figure out the exact function either. If I find anything I'll post the info.

[flea]

Only disabling the master post O2 test does not prevent P0420/430 DTCs (at least on the E40 GTOs)

Based on this it appears the purpose of the master post O2 test is to monitor the performance of these O2 sensors. It does not disable the sensors.

[brantsz]

Sort of off the subject, but if you disable COT and you have DOD it will not request DOD. I also feel it may affect the VVT Cam Phase position also "not 100% sure" I had to turn the COT back on and set the rate to 1.0 and super high COT enable points to get around it.

Catalyst test and Post O2 test are both shut off in my tune. No SES lights. This is with an E38, L76 combo

[etxridn]

Only disabling the master post O2 test does not prevent P0420/430 DTCs (at least on the E40 GTOs)

Based on this it appears the purpose of the master post O2 test is to monitor the performance of these O2 sensors. It does not disable the sensors.

HI.
Old thread I know but since they have removed the options to disable post 02 test, I would like to know what the ecu is actually is doing during this test?

[GHuggins]

Usually post O2 will switch super rich and then super lean for a period of seconds each within 4 minutes of engine runtime - Precat O2 test will happen right after fire up. Cat test "usually" run while at speed and switch fueling normally, but it will look at the rear O2's to make sure they stay the same or don't turn into a sine wave. Once you start removing parts without cutting things off is where it can get interesting because it can get "stuck" lean or rich or even go into open loop... Most GM products will do start the test with the driver's precat O2 then switch to the passenger's precat O2. If driver's fails - it'll usually default open loop. Passenger's fails it'll default to using driver's for both banks. At least that's what I've noticed...