1999 4EAT Transmission Operation
There are seven different shift schedules/
maps in the TCM logic control of
the 1999 Second Generation 4EAT. They
are Normal, Power, Slope, Hold 2nd,
Cruise, Hot ATF, Cold ATF. The shift
schedule/map will determine how and
when the transmission shifts. For example,
in the slope mode, when driving up
a hill under certain engine load conditions,
the TCM will shift the transmission
back down to 3rd gear.
In most cases, the transmission will
stay in 3rd gear until the vehicle reaches
the top of the hill, then it will upshift.
This is done to keep the transmission
from upshifting/downshifting in and out
of 4th gear needlessly. On the uphill
control, the slope angle is estimated
from the throttle opening angle and
vehicle speed change. When the TCU
detects that the vehicle is moving
uphill, upshifting is restrained by selecting
a special shift map, which prevent
needless upshifting/downshifting.
When driving downhill, under coasting
conditions, if the driver touches the
brake pedal, the TCM will downshift the
transmission into 3rd gear to provide
engine braking. This downhill control is
canceled when the TCU detects the
vehicle acceleration by the driver’s
depressing of the accelerator pedal and
input from the Throttle Position Sensor.
Both of these conditions are part of
the slope control logic and are a characteristic
of the vehicle TCM logic.