Gear ratios can be determined by using the scan tool
and reading the Input/Output Speed Sensor values in
the “Monitors” display. Gear ratio can be obtained by
dividing the Input Speed Sensor value by the Output
Speed Sensor value.
For example, if the input shaft is rotating at 1000 rpm
and the output shaft is rotating at 500 rpm, then the
TCM can determine that the gear ratio is 2:1. In direct
drive (3rd gear), the gear ratio changes to 1:1. The
gear ratio changes as clutches are applied and
released. By monitoring the length of time it takes for
the gear ratio to change following a shift request, the
TCM can determine the volume of fluid used to apply
or release a friction element.
The volume of transmission fluid needed to apply the
friction elements are continuously updated for adaptive
controls. As friction material wears, the volume of fluid
need to apply the element increases.
Certain mechanical problems within the input clutch
assembly (broken return springs, out of position snap
rings, excessive clutch pack clearance, improper assembly, etc.) can cause inadequate or out-of-range element vol-
umes. Also, defective Input/Output Speed Sensors and wiring can cause these conditions. The following chart iden-
tifies the appropriate clutch volumes and when they are monitored/updated:
CLUTCH VOLUMES
Clutch
When Updated
Proper Clutch
Volume
Shift Sequence
Oil Temperature
Throttle Angle
L/R
2-1 or 3-1 coast
downshift
> 21° C (70° F)
< 5°
35 to 83
2/4
1-2 shift
> 43° C (110° F)
5 - 54°
20 to 77
OD
2-3 shift
48 to 150
UD
4-3 or 4-2 shift
> 5°
24 to 70
SHIFT SCHEDULES
As mentioned earlier, the TCM has programming that allows it to select a variety of shift schedules. Shift schedule
selection is dependent on the following:
•
Shift lever position
•
Throttle position
•
Engine load
•
Fluid temperature
•
Software level
As driving conditions change, the TCM appropriately adjusts the shift schedule. Refer to the following table 42RLE
Shift Schedule to determine the appropriate operation expected, depending on driving conditions.
42RLE Shift Schedule
Schedule
Condition
Expected Operation
Extreme Cold
Oil temperature at start-up below
-27° C (-16° F)
Park, Reverse, Neutral and 2nd
gear only (prevents shifting which
may fail a clutch with frequent
shifts)
8E - 164
ELECTRONIC CONTROL MODULES
KJ