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 degrees 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, how-
ever 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
9
cold
9
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 sole-
noid 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 gov-
ernor pressure.
GOVERNOR PRESSURE CURVES
LOW TRANSMISSION FLUID TEMPERATURE
When the transmission fluid is cold the conventional governor can delay shifts, resulting in higher than normal shift
speeds and harsh shifts. The electronically controlled low temperature governor pressure curve is higher than nor-
mal to make the transmission shift at normal speeds and sooner. The PCM uses a temperature sensor in the trans-
mission oil sump to determine when low temperature governor pressure is needed.
NORMAL OPERATION
Normal operation is refined through the increased computing power of the PCM and through access to data on
engine operating conditions provided by the PCM that were not available with the previous stand-alone electronic
module. This facilitated the development of a load adaptive shift strategy - the ability to alter the shift schedule in
response to vehicle load condition. One manifestation of this capability is grade
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hunting
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prevention - the ability of
the transmission logic to delay an upshift on a grade if the engine does not have sufficient power to maintain speed
in the higher gear. The 3-2 downshift and the potential for hunting between gears occurs with a heavily loaded
vehicle or on steep grades. When hunting occurs, it is very objectionable because shifts are frequent and accom-
panied by large changes in noise and acceleration.
WIDE OPEN THROTTLE OPERATION
In wide-open throttle (WOT) mode, adaptive memory in the PCM assures that up-shifts occur at the preprogrammed
optimum speed. WOT operation is determined from the throttle position sensor, which is also a part of the emission
control system. The initial setting for the WOT upshift is below the optimum engine speed. As WOT shifts are
repeated, the PCM learns the time required to complete the shifts by comparing the engine speed when the shifts
occur to the optimum speed. After each shift, the PCM adjusts the shift point until the optimum speed is reached.
The PCM also considers vehicle loading, grade and engine performance changes due to high altitude in determining
when to make WOT shifts. It does this by measuring vehicle and engine acceleration and then factoring in the shift
time.
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AUTOMATIC TRANSMISSION - 48RE - SERVICE INFORMATION
DR/DH