Fuel Trims LS1 V8
0 - 15 defined by the LTFT RPM and MAP boundaries
16 - Idle PN (AC on)
17 - Idle PN (AC off)
18 - Idle InGear (AC on)
19 - Idle InGear (AC off)
20 - Idle (EVAP closed)
21 - Coastdown (EVAP closed)
22 - Non-Idle (EVAP Closed)
Usually EVAP closes at WOT hence cell #22 is mostly used at WOT, but you will see it used during warmup (before evap purge begins). At WOT you will also see cell #15 if the EVAP purge opens (ie. vacuum drops enough for the purge to begin).
Fuel Trims LS2/LS7/L76, Cobalt SS 2.0L s/c and other later model vehicles that use RPM/MAP boundaries
The LS2/7 and others have more cells but follow a similar pattern to the LS1:
EVAP Open
0 - 15 defined by the LTFT RPM and MAP boundaries
16 - Idle PN (AC on)
17 - Idle PN (AC off)
18 - Idle InGear (AC on)
19 - Idle InGear (AC off)
20 - Decel
EVAP Closed
21 - 36 defined by the LTFT RPM and MAP boundaries
37 - Idle
38 - Decel
Fuel Trims later LS3 and other later model vehicles that use Airflow Mode boundaries
EVAP Open
0 - 5 defined by the LTFT Airflow Mode Purge On boundaries
6 - Idle
7 - Decel
EVAP Closed
8 - 13 defined by the LTFT Airflow Mode Purge Off boundaries
14 - Idle
15 - Decel
Fuel Trims V6 vehicles
0 = Idle
1 = Decel
2 = Light Load / Engine Not Running
3 = High Load