Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

346 Chapter Fifteen
On any vehicle, perform a visual inspection of
the system. Check the vacuum hoses for disconnects,
pinches, loose connections, etc. Inspect all
wiring for tight, clean connections. Also, look for
good insulation and proper wire routing. Check
the fuses for opens and replace as needed. Check
and adjust linkage cables or chains, if needed.
Some manufacturers require additional preliminary
checks before entering diagnostics. In addition,
perform a road test (or simulated road test)
in compliance with the service manual to confirm
the complaint.
ter or sides of the steering wheel. There are usually
several functions on the switch, including off-on,
resume, and engage buttons. The switch is different
for resume and non-resume systems.
The transducer is a device that controls
the speed of the vehicle. When the transducer is
engaged, it senses vehicle speed and controls a
vacuum source (usually the intake manifold). The
vacuum source is used to maintain a certain position
on a servo. The speed control is sensed from
the lower cable and casing assembly attached to
the transmission.
CAUTION: When servicing the cruise control system, you will be working close to the air bag
and antilock brake systems.The service manual will instruct you when to disarm and/or depressurize
these systems. Failure to follow these procedures can result in injury and additional
costly repairs to the vehicle.
When engaged, the cruise control components
set the throttle position to the desired speed. The
speed is maintained unless heavy loads and steep
hills interfere. The cruise control is disengaged
whenever the brake pedal is depressed. The common
speed or cruise control system components
function in the following manner.
Cruise Control Switch
The cruise control switch (Figure 15-47) is located
on the end of the turn signal lever or near the cen-
The servo unit is connected to the throttle by a
rod or linkage, a bead chain, or a Bowden cable.
The servo unit maintains the desired car speed by
receiving a controlled amount of vacuum from
the transducer. The variation in vacuum changes
the position of the throttle. When a vacuum is
applied, the servo spring is compressed and the
throttle is positioned correctly. When the vacuum
is released, the servo spring is relaxed and the system
is not operating.
Two switches are activated by the position of
the brake pedal. When the pedal is depressed,
the brake-release switch disengages the system.
Figure 15-47.
Cruise control switch.