TM 5-3805-296-23-1
0004
PRIMARY POWERTRAIN SYSTEM
0004
Transmission Control
0004
The tractor has a semi-automatic transmission. Power is transmitted from the engine, to a driveshaft, through
transmission transfer gears, the torque converter, the transmission, and finally to the differential and final drives.
The transmission/chassis ECM regulates shifting of gears. The transmission/chassis ECM receives signals from
the transmission hold switch, the speed sensor, the transmission switch, and the shift lever switch. Based off these
inputs, the ECM commands the upshift solenoid or downshift solenoid. The upshift solenoid and downshift solenoid
control hydraulic oil flow in the transmission controlling direction and gear selection of the transmission. The trans-
mission/chassis ECM monitors the following switches and sensors to determine which gear the transmission
should be in:
Ignition Start Switch - This switch provides battery voltage to the transmission/chassis ECM when the switch
is placed in the ON position. This input also provides power to the start relay.
Transmission Shift Lever Sensor - The sensor for the shift lever provides a PWM signal to the transmission/
chassis ECM. The PWM signal varies with the gear that is selected.
Gear Hold Switch - When the gear hold switch is activated, a signal is sent to the transmission/chassis ECM.
The transmission/chassis ECM hold control prevents all automatic upshifts and downshifts unless an engine
overspeed or engine underspeed condition occurs. This function will not operate in first or second gear.
Top Gear Switch - This switch is used to select the top gear that is desired by the operator. This setting is lim-
ited to the machine's Maximum Drive Gear.
Tractor Actual Gear Switch - This switch provides information on the current transmission gear to the trans-
mission/chassis ECM.
Transmission Output Speed Sensor (TOS 1 and TOS 2) - Two TOS sensors provide the transmission/chas-
sis ECM with the output speed of the transmission.
Engine Output Speed Sensor (EOS) - The EOS provides the transmission/chassis ECM with the output
speed of the engine.
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