The AFR cycle you see there may be the catalyst test being performed... that's exactly what it looks like...
The catalyst monitor transits the AFR and times the voltage response from front O2 sensor to rear O2 sensor (it does each bank simultaneously but independently)... if the response time is shorter than the prescribed minimum then the catalyst efficiency DTC is set (P0420, P0430)... then the AFR goes back to normal control.
The trims are just kept constant during the catalyst test.
how do you shut it off?
"All that is needed for the triumph of evil is that good men do nothing..."
My '08 Trailblazer SS does a similar symptom. It is usually after an extended cruise at highway speeds then slowing to a stop like at a stop light on an off ramp. While sitting stationary, the engine will stumble and I'll notice on the wideband that AFR will go rich (12.5 or so) then swing lean (16.5 or so). It has done that since new with the stock calibration. I've caught it while logging as well and it's being commanded rich and lean when it occurs. I did notice that while staying in speed density open loop when doing my auto VVE and auto MAF that it did not occur. I was thinking it was some kind of O2 rationality test, looks like testing cat efficiency makes sense as well.
I believe the test can't be shut off in closed loop mode (even with DTC disabled, the test still runs, but its results are ignored).
I believe in open loop mode the test is never run.
How about disabling {C1701} Catalyst Diagnostic Test ?
John
C1701 isn't in my file LS1 file.
Sorry Joecar,
I was looking at my E38 stuff.
John
I never noticed that. I'll have to give that a try.Originally Posted by ssvolvo
will do too.... maybe a custom OS to do a lean cruise?
"All that is needed for the triumph of evil is that good men do nothing..."
I had C1701 set to disabled in my log from post #7.
Might have to adjust min and max temps (C1702 & C1703) to really make sure it's disabled.
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