Servo Description; Operation; Removal; Installation - Chrysler 300M Service Manual

LH
SERVO
DESCRIPTION
The servo unit consists of a solenoid valve body,
and a vacuum chamber. The solenoid valve body con-
tains three solenoids:
• Vacuum
• Vent
• Dump
The vacuum chamber contains a diaphragm with a
cable attached to control the throttle linkage.

OPERATION

The PCM controls the solenoid valve body. The
solenoid valve body controls the application and
release of vacuum to the diaphragm of the vacuum
servo. The servo unit cannot be repaired and is ser-
viced only as a complete assembly.
Power is supplied to the servo by the PCM through
the brake switch. The PCM controls the ground path
for the vacuum and vent solenoids.
The dump solenoid is energized anytime it receives
power. If power to the dump solenoid is interrupted,
the solenoid dumps vacuum in the servo. This pro-
vides a safety backup to the vent and vacuum sole-
noids.
The vacuum and vent solenoids must be grounded
by the PCM to operate. When the PCM grounds the
vacuum servo solenoid, the solenoid allows vacuum
to enter the servo and pull open the throttle plate
using the cable. When the PCM breaks the ground,
the solenoid closes and no more vacuum is allowed to
enter the servo. The PCM also operates the vent sole-
noid via ground. The vent solenoid opens and closes a
passage to bleed or hold vacuum in the servo as
required.
The PCM cycles the vacuum and vent solenoids to
maintain the set speed, or to accelerate and deceler-
ate the vehicle. To increase throttle opening, the
PCM grounds the vacuum and vent solenoids. To
decrease throttle opening, the PCM removes the
grounds from the vacuum and vent solenoids.

REMOVAL

(1) Disconnect the negative battery cable.
(2) Remove three bolts from servo bracket.
(3) Disconnect electrical connectors and vacuum
hose.
(4) Remove two nuts attaching speed control cable
and mounting bracket to servo.
(5) Remove servo mounting bracket.
(6) Pull cable away from servo to expose retaining
clip and remove clip attaching cable to servo.

INSTALLATION

(1) With throttle in full open position align hole in
speed control cable sleeve with hole in servo pin and
install retaining clip.
(2) Connect vacuum hose to servo.
(3) Connect electrical connector.
(4) Insert servo studs through holes in speed con-
trol cable and mounting bracket.
(5) Install nuts, tighten to 6.7 N·m (60 in. lbs.).
(6) Install servo and bracket and tighten bolt and
nuts.
(7) Connect negative battery cable.
SWITCH
DESCRIPTION
There are two separate switch pods that operate
the speed control system and are located on the
steering wheel.
OPERATION
The speed control system has five separate resis-
tive switches that provide a single multiplexed
(MUX) voltage inputs to the PCM.The switch names
are: ON, OFF, SET, COAST, RESUME, ACCEL, TAP-
UP, COAST, and CANCEL. Based on conditions when
the buttons are pushed (and released), the five volt-
ages ranges provided to the PCM result in the follow-
ing functions: ON, OFF, SET, COAST, RESUME,
ACCEL, TAP-UP, TAP-DOWN, COAST, and CAN-
CEL. Refer to the Speed Control Section for more
information
Also the PCM receives an input from the brake
switch to sense whether the brake pedal has been
depressed. When the PCM receives the brake
depressed input, it turns off power to the speed con-
trol servo and disengages speed control. Also the
power to the servo is supplied through the brake
switch, which opens the circuit when the brake pedal
is depressed.
The individual switches cannot be repaired. If one
switch fails, the entire switch module must be
replaced.
REMOVAL
The speed control switch is mounted in the steer-
ing wheel and wired through the clock spring device
under the airbag module.
WARNING: IF REMOVAL OF AIRBAG MODULE IS
NECESSARY, REFER TO THE RESTRAINT SYS-
TEMS SECTION FOR MORE INFORMATION.
(1) Remove the negative battery cable.
(2) Turn off ignition.
SPEED CONTROL 8P - 5