THEORY OF OPERATION - CONTINUED
POWERTRAIN - CONTINUED
Sensors. Sensors provide information to powertrain ECM about changing conditions. Sensor signals change pro-
portionally to changing conditions. Powertrain ECM recognizes frequency signals (frequency (Hz) of sensor signal
varies as condition changes) and pulse width modulated (PWM) signals (duty cycle of sensor signal varies as con-
dition changes; frequency of this signal is constant).
There are two transmission speed sensors and torque converter output speed sensor on machine. Speed
sensors are powertrain ECM inputs. These speed sensors are frequency sensors which produce a signal
(Hz) which varies as conditions change. Sensor generates an approximate sine wave signal from gear teeth
as gear teeth pass sensor. Sensor produces a signal equal to one pulse per gear tooth. This signal is sent to
powertrain ECM, which measures signal frequency to determine speed. With dual sensors, powertrain
ECM receives signals from speed sensors and uses difference in input from speed sensors to determine
system direction. Powertrain ECM uses speed sensor input to regulate transmission shifts. Each speed sen-
sor has two powertrain ECM connections (+ and -).
N OT E
The speed sensors are used to diagnose each other during normal operation. The powertrain ECM periodi-
cally checks the value from the speed sensor. If an incorrect value is found, the powertrain ECM will log a
service code that indicates a fault for a speed sensor circuit.
Powertrain ECM sends speed information to other ECMs via CAT Data Link. For all speed sensors, con-
nector contact 2 is signal line and connector contact 1 is return line. Two intermediate speed sensors mea-
sure intermediate transmission speed. Two transmission speed sensors measure transmission output speed.
Powertrain ECM uses pairs of speed sensors to determine rotation direction.
Temperature Sensor (Transmission Oil). Transmission oil temperature sensor is a passive sensor. As oil
temperature changes, sensor resistance will change. This change in resistance changes voltage seen by
powertrain ECM. Powertrain ECM measures transmission oil temperature from voltage of transmission oil
temperature sensor. Powertrain ECM uses oil temperature reading to adjust transmission shift times. Pow-
ertrain ECM adjusts transmission shift times to provide smooth shifts over various ranges of transmission
Position Sensor (Left Brake Pedal).
(a) Position sensor (left brake pedal) sends an input to ECM. Sensor will continuously update powertrain
ECM on position of left brake pedal. Left pedal position sends a change in input signal to powertrain
ECM, which records change of position, then activates appropriate solenoid valve.
(b) Position sensor (left brake pedal) is a PWM sensor which continuously generates a PWM signal. Duty
cycle varies in proportion to lever position. ECM receives PWM signal from position sensor and mea-
sures duty cycle to determine lever position. Sensor signal frequency is constant at 500 Hz. Machine
electrical system provides +battery voltage to lever position sensor for operating power.
Start relay is a powertrain ECM output. Activation and deactivation of start solenoid is start relay's pur-
pose. Start solenoid controls starting motor.
When operator turns engine start switch to START and powertrain ECM decides all starting conditions are
satisfied, powertrain ECM activates start relay with a +battery signal at connector contact J2-1. Operator
must also have direction switch in NEUTRAL. When all starting conditions are satisfied, powertrain ECM
sends a +battery signal to connector contact J2-7 for start relay and engine cranking begins.
Terminal 3 of start relay contacts to a +battery source. Terminal 4 connects to start solenoid.