THEORY OF OPERATION - CONTINUED
POWERTRAIN - CONTINUED
For transmission to shift automatically, autoshift switch must be in one of two AUTO positions and left brake
pedal must be fully released. Powertrain ECM shifts transmission automatically after evaluating input sent from
engine speed sensor, transmission speed sensors, torque converter output speed sensor, and left brake pedal posi-
tion sensor to regulate transmission shifts. Powertrain ECM does not allow upshifts to a speed higher than speed
selected by transmission direction and shift lever. An automatic downshift from second to first speed occurs only if
autoshift switch is in "1-4" position (TM 5-3805-291-10).
Table 2. Automatic Upshift and Downshift.
Speed Range and
1F to 2F
2F to 3F
3F to 4F
4F to 3F
3F to 2F
2F to 1F
1R to 2R
2R to 3R
3R to 4R
4R to 3R
3R to 2R
2R to 1R
The speeds listed are approximate and should be used for reference only.
When transmission downshift switch is depressed, transmission downshift switch signals powertrain ECM to
downshift transmission by one speed. Pressing and holding transmission downshift switch signals powertrain
ECM to continue to downshift transmission as machine speed decreases. Powertrain ECM delays resuming auto-
matic upshifts for five seconds after transmission downshift switch is released. Automatic upshifts are enabled if
transmission direction and shift lever is moved from current direction and left brake pedal is not depressed. Mov-
ing transmission direction and shift lever or five-second delay will enable automatic upshifts.
When engine start switch is turned from OFF to ON, powertrain ECM is activated. When powertrain ECM is first
activated, all modulating valves (transmission clutch) are de-energized regardless of transmission direction and
shift lever position. Powertrain ECM then determines if transmission direction and shift lever is in NEUTRAL. If
NEUTRAL is not selected, powertrain ECM disables transmission. Transmission direction and shift lever must be
returned to NEUTRAL before a direction can be selected. Powertrain ECM activates start relay, allows engine to
start, and allows initial selected speed to be changed if transmission direction and shift lever is in NEUTRAL.