Copyright by Goodheart-Willcox Co., Inc.
202 Automatic Transmissions and Transaxles
Ignition key
Key cylinder
Camshaft
Key lock solenoid
Lock
pin
Figure 9-23. This solenoid is installed on the ignition key assembly and is operated by a small computer. It prevents accidental starts
in gear and reduces the chance of vehicle theft. (Lexus)
Selector
lever button
Grooved pin
Shift lock
override button
Shift lock
computer
Shift lock solenoid
Plate stopper
Shift lock
override link
Shift lock
control
switch
Shift lock
plate
Figure 9-24. This shift-brake interlock uses a small computer
and a solenoid to prevent damage to the drive train and engine.
The shift selector lever is connected to a small computer. The
computer triggers the solenoid, which will not allow the lever to
be moved out of gear unless the brake is applied. (Lexus)
Computer
Oil passage
Block
Electrical connection
Electrical
contacts
Diaphragm
Figure 9-25. The typical hydraulic pressure sensor is a switch
that tells the computer that a hydraulic circuit is pressurized. Oil
pressure acts on the switch diaphragm to open or close the
electrical contacts.
Electrical Components
Modern transmission hydraulic systems have electrical
and electronic components. On newer vehicles, electrical
and electronic components control all transmission func-
tions, including gear changes. Some of the more common
components are discussed below. These components and
the devices that control them will be discussed in more
detail in Chapter 12.
Switches
Switches use electrical contacts to energize or de-
energize a solenoid or motor, or to send an electrical signal
to another electrical device. Switches generally have two
contacts. When the contacts are touching, the switch is in
the on position and current can flow through the switch.
When the contacts are separated, the switch is in the off
position and current cannot flow. Some pressure switches
have one contact, and current flow is grounded through the
switch body in the on position.
The driver activates some switches through shift link-
age connected to the gear selector lever. Another type of
driver-operated switch is installed on the accelerator linkage
to operate the detent (passing gear) valve system. These types
of switches are discussed in more detail later in this chapter.
Another commonly used switch is the pressure switch.
Modern transmissions usually contain several pressure
switches. Pressure switches are opened and closed by
transmission hydraulic pressures, Figure 9-25. Figure 9-26
illustrates a typical pressure switch and its general location
on the valve body.