Transmission Fluid
Transmission fluid is a combination of petroleum oils
and various additives. It is pressurized by the pump and
used to operate the hydraulic system. Since the trans-
mission fluid splashes on the holding members, it contains
additives that help the holding members to grip when they
are applied. Transmission fluid also lubricates gears, bear-
ings, and moving parts. Some transmission parts are lub-
ricated by fluid under pressure. Other components depend
on splash lubrication. Transmission fluid also carries away
heat and helps seal in pressure.
There are several types of transmission fluid used in
modern vehicles. Proper fluid is important to transmission
and transaxle operation. At one time, almost all automatic
transmissions and transaxles used the same type of fluid.
Today, however, many domestic and imported vehicles
use special fluids. Never add transmission fluid to any
automatic transmission or transaxle without first finding
out what type of fluid should be used. Some manufacturers
allow the use of a common fluid, such as Dexron III, if a
special friction modifier is added to the fluid.
Chapter 1 Introduction to Automatic Transmissions and Transaxles 27
+
+
–
–
Map/baro sensor
Air conditioning
clutch (ACC)
Engine RPM sensor
(RPM sensor)
(diesel engines)
Profile ignition pickup
(PIP) from distributor
engine RPM
(gasoline engine)
Brake on/off
(BOO) switch
Programmable
speedometer/odometer
module (PSOM)
Manual level
position (MLP)
sensor
Transmission oil
temperature
(TOT) sensor
Vehicle speed
sensor (VSS)
4x4 low
(4x4 L)
Transmission
solenoid body
–SS1
–SS2
–EPC
–TCC
–CCS
RABS
speed
sensor
Rear
anti-lock
brake
module
Speed
control
module
PSOM
VSS (+)
PCM
VSS (–)
Malfunction
indicator
lamp (MIL)
Transmission control
indicator lamp (TCIL)
Powertrain
control module
(PCM)
Throttle
position (TP)
sensor
Input/output
(1989-1991
model transmissions)
(1992 and 1993 model
transmissions)
Figure 1-31. The computer that controls a modern transmission or transaxle is connected to many input sensors and output
devices. In some vehicles, a single computer may be used to control the transmission or transaxle, the engine, and other
systems. (Ford)