RAM 3500 Truck 2WD V10-8.0L VIN W HDC (2000)
control engagement of the fourth gear overdrive clutch, the converter clutch, and governor pressure. Normal resistance value for the thermistor at
room temperature is approximately 1000 ohms.
The thermistor is part of the governor pressure sensor assembly and is immersed in transmission fluid at all times.
TRANSMISSION SPEED SENSOR
Fig. 67
The speed sensor (Fig. 67) is located in the overdrive gear case. The sensor is positioned over the park gear and monitors transmission output shaft
rotating speed.
OPERATION
Compensation is required for performance variations of two of the input devices. Though the slope of the transfer functions is tightly controlled, offset
may vary due to various environmental factors or manufacturing tolerances.
The pressure transducer is affected by barometric pressure as well as temperature. Calibration of the zero pressure offset is required to compensate for
shifting output due to these factors.
Normal calibration will be performed when sump temperature is above 50°F, or in the absence of sump temperature data, after the first 10 minutes of
vehicle operation. Calibration of the pressure transducer offset occurs each time the output shaft speed falls below 200 RPM. Calibration shall be
repeated each 3 seconds the output shaft speed is below 200 RPM. A 0.5 second pulse of 95% duty cycle is applied to the governor pressure solenoid
valve and the transducer output is read during this pulse. Averaging of the transducer signal is necessary to reject electrical noise.
Under cold conditions (below 50°F sump), the governor pressure solenoid valve response may be too slow to guarantee 0 psi during the 0.5 second
calibration pulse. Calibration pulses are continued during this period, however the transducer output valves are discarded. Transducer offset must be
read at key-on, under conditions which promote a stable reading. This value is retained and becomes the offset during the "cold" period of operation.
GOVERNOR PRESSURE SOLENOID VALVE
The inlet side of the solenoid valve is exposed to normal transmission line pressure. The outlet side of the valve leads to the valve body governor
circuit.
The solenoid valve regulates line pressure to produce governor pressure. The average current supplied to the solenoid controls governor pressure. One
amp current produces zero kPa/psi governor pressure. Zero amps sets the maximum governor pressure.
The Powertrain Control Module (PCM) turns on the trans control relay which supplies electrical power to the solenoid valve. Operating voltage is 12
volts (DC). The PCM controls the ground side of the solenoid using the governor pressure solenoid control circuit.
GOVERNOR PRESSURE SENSOR
The sensor output signal provides the necessary feedback to the PCM. This feedback is needed to adequately control governor pressure.
GOVERNOR BODY AND TRANSFER PLATE
The transfer plate channels line pressure to the solenoid valve through the governor body. It also channels governor pressure from the solenoid valve
to the governor circuit. It is the solenoid valve that develops the necessary governor pressure.
TRANSMISSION FLUID TEMPERATURE THERMISTOR
The PCM prevents engagement of the converter clutch and overdrive clutch, when fluid temperature is below approximately 10°C (50°F).
If fluid temperature exceeds 126°C (260°F), the PCM causes a 4-3 downshift and engage the converter clutch. Engagement is according to the third
gear converter clutch engagement schedule.
The overdrive OFF lamp in the instrument panel illuminates when the shift back to third occurs. The transmission will not allow fourth gear operation
until fluid temperature decreases to approximately 110°C (230°F).
TRANSMISSION SPEED SENSOR
Speed sensor signals are triggered by the park gear lugs as they rotate past the sensor pickup face. Input signals from the sensor are sent to the
transmission control module for processing. The vehicle speed sensor also serves as a backup for the transmission speed sensor. Signals from this
sensor are shared with the powertrain control module.
