brakes DODGE NEON 2000 Service Owners Manual

(5) Disconnect the primary and secondary brake
tubes from master cylinder (Fig. 12). Install plugs in
the master cylinder outlet ports.
(6) Clean the area around where the master cylin-
der attaches to the power brake booster using a suit-
able brake cleaner such as MopartBrake Parts
Cleaner or an equivalent.
(7) Remove the 2 nuts attaching master cylinder to
power brake booster (Fig. 12).
(8) Slide the master cylinder straight out of the
power brake booster.
INSTALLATION
NOTE: The master cylinder must be bled before
installing it on the vehicle.
(1) Bleed the master cylinder before installing it
on the vehicle. Refer to MASTER CYLINDER
BLEEDING in SERVICE PROCEDURES within this
section of this service manual group.
(2) Wipe the face of the power brake booster clean
where the master cylinder seal comes in contact
when it's installed. Do not get any cleaner or debris
inside the booster.(3) Position the master cylinder on the studs of
power brake vacuum booster aligning the booster
push rod with the master cylinder push rod. Care-
fully push the master cylinder onto the studs until it
contacts the face of the booster.
(4) Install the two master cylinder mounting nuts
(Fig. 12). Tighten the mounting nuts to a torque of
28 N´m (250 in. lbs.).
(5) Connect the primary and secondary brake
tubes to the master cylinder primary and secondary
ports (Fig. 12). Tighten the nuts to a torque of 17
N´m (145 in. lbs.).
(6) Install the wiring harness connector on the
master cylinder reservoir fluid level switch.
(7) Install the battery and clamp in place.
(8) Connect the positive, then the negative
(ground) cable on the battery.
(9) Fill the master cylinder to the proper fill level.
(10) Road test the vehicle to ensure proper opera-
tion of the base and antilock brake systems.
INTEGRATED CONTROL UNIT
NOTE: Before proceeding with this procedure,
review SERVICE WARNINGS AND CAUTIONS at the
beginning of REMOVAL AND INSTALLATION in this
section.
REMOVAL
(1) Using a brake pedal holder, depress the brake
pedal past its first one inch of travel and hold it in
this position (Fig. 13). This will isolate the master
cylinder from the brake hydraulic system and will
not allow the brake fluid to drain out of the master
cylinder reservoir.
(2) Disconnect negative (ground) cable from the
battery and isolate the cable.
(3) Disconnect the positive cable from the battery,
then remove the battery from the battery tray. There
is one nut securing the clamp on the backside of the
battery holding it in place.
(4) Remove the one nut and one bolt securing the
air cleaner box in place, then disconnect the wiring
harness connector at the air inlet sensor.
(5) Lift the air cleaner box upward enough to clear
its grommeted alignment post (Fig. 14), then move
the air cleaner box forward just enough to access the
battery tray mounting bolts.
(6) Remove the 2 bolts, then the 2 nuts mounting
the battery tray to its bracket (Fig. 14). Remove the
battery tray.
Fig. 12 Master Cylinder
1 ± POWER BRAKE BOOSTER
2 ± CONNECTOR
3 ± BRAKE FLUID LEVEL SWITCH
4 ± MOUNTING NUTS
5 ± SECONDARY BRAKE TUBE
6 ± PRIMARY BRAKE TUBE
PLBRAKES 5 - 79
REMOVAL AND INSTALLATION (Continued)

(7) Disconnect the primary and secondary brake
tubes from the master cylinder (Fig. 15). Install
plugs in the master cylinder outlet ports.
(8) Disconnect the 25-way connector from the con-
troller antilock brake (CAB) mounted on the inte-
grated control unit (ICU) and move it out of the way.
The connector is disconnected by pulling outward on
the connector lock (Fig. 16). This will unlock and
raise the 25-way connector out of the socket on the
CAB.(9) Tag the brake tubes coming from the master
cylinder as primary and secondary (Fig. 15). This is
done to avoid mix-up once the tubes are removed
from the vehicle.
(10) Disconnect and remove the primary and sec-
ondary brake tubes coming from the master cylinder
at the ICU hydraulic control unit (HCU) (Fig. 15).
(11) Disconnect the brake tubes going to each indi-
vidual brake at the HCU (Fig. 15).
(12) Remove the 3 bolts attaching the ICU to its
mounting bracket (Fig. 17).
(13) Remove the ICU from the vehicle.
Fig. 13 Brake Pedal Holder
1 ± CLUTCH PEDAL (IF EQUIPPED WITH MANUAL TRANSAXLE)
2 ± THROTTLE PEDAL
3 ± BRAKE PEDAL HOLDING TOOL
4 ± STEERING WHEEL
5 ± DRIVER'S SEAT
6 ± BRAKE PEDAL
Fig. 14 Battery Tray Mounting
1 ± BATTERY TRAY MOUNTING NUTS
2 ± BATTERY TRAY MOUNTING BOLTS
3 ± AIR CLEANER BOX POST
Fig. 15 Brake Tube Locations
1 ± PRIMARY BRAKE TUBE
2 ± SECONDARY BRAKE TUBE
3 ± BRAKE TUBES FROM MASTER CYLINDER
4 ± BRAKE TUBES TO BRAKES
Fig. 16 Connector Lock Pulled Outward
1 ± MASTER CYLINDER
2 ± 25±WAY CONNECTOR
3 ± CAB
4 ± CONNECTOR LOCK PULLED OUTWARD
5 ± ICU
5 - 80 BRAKESPL
REMOVAL AND INSTALLATION (Continued)

(14) Refer to DISASSEMBLY AND ASSEMBLY in
this section of this group for the procedure on sepa-
rating and reattaching the CAB to the HCU.
INSTALLATION
(1) Install the ICU onto its mounting bracket.
(2) Install the 3 bolts attaching the ICU to the
mounting bracket (Fig. 17). Tighten the 3 mounting
bolts to a torque of 11 N´m (97 in. lbs.)
(3) Install the four brake tubes going to the brakes
into their respective outlet ports on the ICU HCU
(Fig. 15). Using a crow foot on a torque wrench,
tighten the four brake tube nuts to a torque of 17
N´m (145 in. lbs.).
NOTE: When installing the brake tubes from the
master cylinder on the HCU, the brake tube with the
small tube nut is to be installed in the forward-most
port on the HCU with the small end going toward
the master cylinder secondary port.
(4) Install the primary and secondary brake tubes
from the master cylinder onto the HCU (Fig. 15). Do
not completely tighten the primary and secondary
tubes at this time.
(5) Connect the primary and secondary brake
tubes to the master cylinder ports (Fig. 15).
(6) Using a crow foot on a torque wrench, tighten
the primary and secondary brake tube nuts at both
the master cylinder and HCU to a torque of 17 N´m
(145 in. lbs.).
CAUTION: Before installing the 25-way connector
in the CAB, be sure the seal is properly installed in
the connector.(7) Install the 25-way connector into the socket of
the CAB as follows:
²Position the 25-way connector in the socket of
the CAB and carefully push it down as far as possi-
ble (Fig. 16).
²When the connector is fully seated into the CAB
socket, push the connector lock inward. This pulls
the connector into the socket of the CAB and locks it
in the installed position.
(8) Position the battery tray back in place. Install
the two bolts, then the two nuts mounting the bat-
tery tray to its bracket (Fig. 14). Tighten the two
bolts and nuts to a torque of 15 N´m (135 in. lbs.).
(9) Reinstall the air cleaner box onto its grom-
meted alignment post (Fig. 14).
(10) Install the one nut and one bolt securing the
air cleaner box in place, then connect the wiring har-
ness connector at the air inlet sensor.
(11) Install the battery and clamp it in place.
Tighten the hold-down clamp bolt to a torque of 12
N´m (105 in. lbs.).
(12) Connect the positive, then the negative
(ground) cable on the battery.
(13) Bleed the base and the ABS hydraulic sys-
tems. Refer to ANTILOCK BRAKE SYSTEM
BLEEDING in this section of this service manual
group.
(14) Fill the master cylinder to the proper fill
level.
(15) Road test the vehicle to ensure proper opera-
tion of the base and antilock brake systems.
WHEEL SPEED SENSOR (FRONT)
NOTE: Before proceeding with this procedure,
review SERVICE WARNINGS AND CAUTIONS at the
beginning of REMOVAL AND INSTALLATION in this
section.
REMOVAL
(1) Raise the vehicle. Refer to HOISTING in the
LUBRICATION AND MAINTENANCE group for the
proper lifting procedure.
(2) Disconnect the wheel speed sensor cable con-
nector from the wiring harness on the inside of the
frame rail above the front suspension crossmember
(Fig. 18). The connector has a locking tab which that
must be pulled back before the connector release
tang can be depressed, releasing the connection.
(3) Remove the speed sensor cable grommet from
the retaining bracket attached to the brake hose on
the outside of the frame rail.
(4) Remove the bolt mounting the wheel speed sen-
sor head to the steering knuckle (Fig. 19).
Fig. 17 ICU Mounting Bolts
1 ± ICU
2 ± ICU MOUNTING BOLTS
PLBRAKES 5 - 81
REMOVAL AND INSTALLATION (Continued)

CAUTION: When removing a wheel speed sensor
from the knuckle, do not use pliers on the sensor
head. This may damage the sensor head. If the sen-
sor has seized, use a hammer and a punch to tap
the edge of the sensor head ear, rocking the sensor
side-to-side until free.
(5) Carefully, remove the sensor head from the
steering knuckle.(6) Remove the screw securing the wheel speed
sensor to the rear of the strut (Fig. 20). Remove the
wheel speed sensor.
INSTALLATION
CAUTION: Failure to install speed sensor cables
properly may result in contact with moving parts or
an over extension of cables causing an open cir-
cuit. Be sure that cables are installed, routed, and
clipped properly.
(1) Attach the wheel speed sensor to the strut
using the its mounting screw (Fig. 20).
(2) Install the wheel speed sensor head in the
steering knuckle (Fig. 19). Install the mounting bolt.
Tighten the mounting bolt to a torque of 12 N´m (105
in. lbs.).
(3) From the sensor bracket on the strut, loop the
sensor cable upward, then downward at the outside
of the frame rail. Install the speed sensor cable grom-
met onto the retaining bracket attached to the brake
hose on the outside of the frame rail.
(4) Loop the wheel speed sensor cable around the
bottom of the frame rail and connect it to the wiring
harness connector on the inside of the frame rail
(Fig. 18). Remember to push in the locking tab on the
connector.
(5) Install the tire and wheel assembly.
(6) Lower the vehicle.
(7) Road test vehicle to ensure proper operation of
the base brakes and ABS.
Fig. 18 Wiring Harness Connector
1 ± RIGHT FRONT WHEEL SPEED SENSOR CONNECTOR
2 ± RIGHT FRONT DRIVESHAFT
3 ± ENGINE OIL FILTER
Fig. 19 Wheel Speed Sensor
1 ± RIGHT FRONT WHEEL SPEED SENSOR
2 ± TONE WHEEL
Fig. 20 Wheel Speed Sensor At Strut
1 ± ABS WHEEL SPEED SENSOR ROUTING BRACKET (IF
EQUIPPED)
2 ± GROUND STRAP
3 ± GROUND STRAP SCREW
4 ± ABS SENSOR BRACKET SCREW (IF EQUIPPED)
5 - 82 BRAKESPL
REMOVAL AND INSTALLATION (Continued)

WHEEL SPEED SENSOR (REAR)
NOTE: Before proceeding with this procedure,
review SERVICE WARNINGS AND CAUTIONS at the
beginning of REMOVAL AND INSTALLATION in this
section.
REMOVAL
(1) Raise the vehicle. Refer to HOISTING in the
LUBRICATION AND MAINTENANCE group for the
proper lifting procedure.
(2) Remove the tire and wheel assembly from the
vehicle.
(3) Disconnect the wheel speed sensor cable con-
nector from the vehicle wiring harness (Fig. 21).
Remove the clip attaching wheel speed sensor cable
connector to the vehicle's body.
(4) Remove the wheel speed sensor cable routing
bracket from under rear brake flex hose mounting
bracket. Then remove the speed sensor cable from
the routing clips on the rear brake flex hose and
chassis brake tube.
(5) Remove the bolt attaching the wheel speed sen-
sor cable routing bracket to rear strut.
CAUTION: When removing a wheel speed sensor
from the rear disc brake adapter, do not use pliers
on the sensor head. This may damage the sensor
head. If the sensor has seized, use a hammer and apunch to tap the edge of the sensor head ear, rock-
ing the sensor side-to-side until free.
(6) Remove the bolt attaching the wheel speed sen-
sor to the rear disc brake adapter (Fig. 22), then
carefully remove the sensor head from the rear disc
brake adapter and vehicle.
INSTALLATION
CAUTION: Failure to install speed sensor cables
properly may result in contact with moving parts or
an over extension of cables causing an open cir-
cuit. Be sure that cables are installed, routed, and
clipped properly.
(1) Install the wheel speed sensor head into the
disc brake adapter (Fig. 22).
(2) Install the wheel speed sensor mounting bolt.
Tighten the mounting bolt to a torque of 12 N´m (105
in. lbs.).
(3) Install the wheel speed sensor cable routing
bracket on the rear strut.
(4) Install wheel speed sensor cable into the rout-
ing clips on the rear brake hose and brake tube.
(5) Connect the wheel speed sensor cable connector
into vehicle wiring harness (Fig. 21). Install the clip
attaching the wheel speed sensor cable connector to
vehicle's body.
(6) Install the tire and wheel assembly on vehicle.
(7) Lower the vehicle.
(8) Road test the vehicle to ensure proper opera-
tion of the base brakes and ABS.
Fig. 21 Wheel Speed Sensor Connector
1 ± FUEL TANK
2 ± TENSION STRUT
3 ± WHEEL SPEED SENSOR CONNECTOR
4 ± LOCKING TAB
5 ± CLIP
Fig. 22 Rear Wheel Speed Sensor
1 ± RIGHT REAR WHEEL SPEED SENSOR
2 ± TENSION STRUT
PLBRAKES 5 - 83
REMOVAL AND INSTALLATION (Continued)

DISASSEMBLY AND ASSEMBLY
INTEGRATED CONTROL UNIT
REMOVAL
NOTE: To replace the hydraulic control unit (HCU)
or the controller antilock brake (CAB) on this vehi-
cle, the entire integrated control unit (ICU) needs to
be removed from the vehicle. The CAB can then be
separated from the HCU. Do not attempt to replace
the CAB with the ICU mounted in the vehicle.
(1) Remove the ICU from the vehicle. Refer INTE-
GRATED CONTROL UNIT in the REMOVAL AND
INSTALLATION section in this section of the service
manual.
(2) Disconnect the pump/motor wiring harness
(Fig. 23) from the CAB.
(3) Remove the 4 bolts (Fig. 24) attaching the CAB
to the HCU.
(4) Remove the CAB from the HCU (Fig. 25).
INSTALLATION
(1) Install the CAB (Fig. 25) on the HCU.(2) Install the 4 bolts mounting the CAB (Fig. 24)
to the HCU. Tighten the CAB mounting bolts to a
torque of 2 N´m (17 in. lbs.).
(3) Plug the pump/motor wiring harness into the
CAB (Fig. 23).
(4) Install the ICU in the vehicle.
(5) Bleed the base and ABS hydraulic systems.
Refer to ANTILOCK BRAKE SYSTEM BLEEDING
in this section of this service manual group.
(6) Road test the vehicle to ensure proper opera-
tion of the base brakes and ABS.
Fig. 23 Pump/Motor To CAB Wiring Harness
1 ± CAB
2 ± PUMP MOTOR WIRING HARNESS
3 ± PUMP MOTOR
4 ± HCU VALVE BLOCK
Fig. 24 CAB Attaching Bolts
1 ± MOUNTING BOLTS
2 ± CAB
3 ± HCU VALVE BLOCK
Fig. 25 Remove/Install CAB
1 ± CAB
2 ± HCU VALVES
3 ± HCU VALVE BLOCK
5 - 84 BRAKESPL

SPECIFICATIONS
TONE WHEEL RUNOUT
FRONT TONE WHEEL:
Maximum Runout.........0.25 mm (0.009 in.)
REAR TONE WHEEL:
Maximum Runout.........0.25 mm (0.009 in.)
WHEEL SPEED SENSOR-TO-TONE WHEEL
CLEARANCE
FRONT WHEEL:
Minimum Clearance.......0.28 mm (0.011 in.)
Maximum Clearance.......1.42 mm (0.056 in.)
REAR WHEEL:
Minimum Clearance.......0.45 mm (0.018 in.)
Maximum Clearance.......1.12 mm (0.044 in.)
BRAKE FASTENER TORQUE SPECIFICATIONS
DESCRIPTION TORQUE
BRAKE TUBES:
Tube Nuts............... 17N´m(145 in. lbs.)
MASTER CYLINDER:
Mounting Nuts.......... 28N´m(250 in. lbs.)
POWER BRAKE BOOSTER:
Mounting Nuts.......... 34N´m(300 in. lbs.)
DISC BRAKE CALIPER:
Caliper Banjo Bolt......... 48N´m(35ft.lbs.)
Guide Pin Bolts.......... 22N´m(192 in. lbs.)
Bleeder Screw........... 15N´m(125 in. lbs.)
WHEEL CYLINDER (REAR):
Mounting Bolts.......... 13N´m(115in.lbs.)
Bleeder Screw............ 10N´m(80in.lbs.)
DRUM BRAKE SHOE SUPPORT PLATE
(REAR):
Mounting Bolts........... 75N´m(55ft.lbs.)
DISC BRAKE ADAPTER (REAR):
Mounting Bolts........... 75N´m(55ft.lbs.)
HUB AND BEARING (REAR):
Retaining Nut.......... 217N´m(160 ft. lbs.)
PARKING BRAKE:
Lever Mounting Nuts..... 28N´m(250 in. lbs.)
TIRE AND WHEEL:
Wheel Mounting Nut...........109±150 N´m
(80±110 ft. lbs.)
INTEGRATED CONTROL UNIT:
Mounting Bolts........... 11N´m(97in.lbs.)
CAB Mounting bolts........ 2N´m(17in.lbs.)
Bracket-to-Frame Rail Bolts.......... 23N´m
(200 in. lbs.)
WHEEL SPEED SENSOR:
Head Mounting bolt...... 12N´m(105 in. lbs.)
PLBRAKES 5 - 85

CONDITION POSSIBLE CAUSE CORRECTION
TEMPERATURE GAUGE READS
HIGH OR ENGINE COOLANT
WARNING LAMP ILLUMINATES.
COOLANT MAY OR MAY NOT BE
LOST FROM SYSTEM. (CONT.)6. Poor seals at radiator cap. 6. (a) Check condition of cap and
cap seals. Refer to Radiator cap
Inspection. Replace cap if
necessary.
(b) Check condition of filler neck. If
neck is bent or damaged, replace
neck.
7. Coolant level low in radiator, but
not in coolant recovery/reserve
container. This indicates the
radiator is not drawing coolant from
the coolant recovery/reserve
container as the engine cools. As
the engine cools, a vacuum is
formed inside the cooling system. If
the radiator cap seals are defective,
or the cooling system has a leak, a
vacuum cannot be formed.7. (a) Check condition of radiator
cap and cap seals. Replace cap if
necessary.
(b) Check condition of filler neck.
Replace if damaged.
(c) Check condition of hose from
filler neck to coolant container. It
should be tight at both ends without
any kinks or tears. Replace hose as
necessary.
(d) Check coolant recovery/reserve
container and hose for blockage.
Repair as necessary.
8. Freeze point of coolant not
correct. Mixture ratio may be too
rich.8. Check coolant concentration.
Refer to Coolant Concentration
Testing in this section. Adjust
glycol-to-water ration as required.
9. Coolant not flowing through
system.9. Check for coolant flow at filler
neck with some coolant removed,
engine warm, and thermostat open.
Coolant should be observed flowing
through filler neck. If flow is not
observed, determine reason for lack
of flow and repair as necessary.
10. Radiator or A/C condenser fins
are dirty or clogged.10. Clean obstruction from fins.
11. Radiator core is plugged or
corroded.11. Replace or re-core radiator.
12. Fuel or ignition system
problems.12. Refer to Fuel and Ignition
System groups for diagnosis. Also
refer to the appropriate Powertrain
Diagnostic Procedure manual.
13. Dragging Brakes. 13. Inspect brake system and repair
as necessary. Refer to Group 5,
Brakes for diagnosis.
14 Bug screen or other aftermarket
accessory is being used causing
reduced air flow.14. Remove bug screen or
accessory.
15. Thermostat partially or
completely closed. This is more
prevalent on high mileage vehicles.15. Check thermostat operation and
replace as necessary. Refer to
thermostat in this section for
procedure.
7 - 8 COOLING SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

DESCRIPTION AND OPERATION
HEADLAMP SWITCH
The headlamp switch is part of the Multi-Function
Switch. Refer to Group 8J, Turn Signal and Flasher
for the Multi-Function Switch Test, Removal and
Installation procedures.
INSTRUMENT CLUSTER
There are two conventional instrument cluster
assemblies available. The clusters electronically drive
the speedometer, odometer, gauges, and tachometer
(if equipped). Refer to (Fig. 2) and (Fig. 3).
The instrument cluster controls the courtesy
lamps, it receives and sends messages to other mod-
ules via the PCI bus circuit, it controls all the instru-
ment illumination and the chime is also an integral
part of the cluster. The front turn signals are wired
through the cluster and then go to the front lamps.
The reason being that the DRL module is built into
the cluster (if equipped).
All gauges in the electronic clusters are the analog
type gauges. When the ignition switch is moved to
the OFF position, the cluster drives each gauge to its
lowest position. The individual gauges are not servi-
cable and require complete replacement of the cluster
if one or more gauges are inoperable.
One button is used to switch the display from trip
to total mileage. Holding the button when the display
is in the trip mode will reset the trip mileage. This
button is also used to put the cluster in self-diagnos-
tic mode. Refer to Service Procedures, Cluster Self-
Diagnostics in this section. Most of the indicators will
come on briefly for a bulb heck when the ignition is
turned from OFF to ON. All of the LED's are replace-
able.
In the event that the instrument cluster looses
communication with all other modules on the PCI
bus, the cluster will display ªnobusº in the VF dis-
play. The VF display also displays ªDoorº, ªCruiseº,
ªTracº, and odometer trip or total.
If the cluster does not detect voltage on the cour-
tesy lamp circuit, the message ªFUSEº will alternate
with the odometer/trip odometer for 30 seconds after
the ignition is turned on and for 15 seconds after the
vehicle is first moved. The lack of voltage can be due
to the M1 Fused B(+) (IOD) fuse being open, a bad or
missing courtesy lamp bulb, or a circuit problem.
WARNING AND INDICATOR LAMPS
The instrument cluster has warning lamps and
indicators for the following systems:
²Airbag
²Anti-lock Brakes (ABS) if equipped
²Brake warning
²Charging System²Front fog lamps (if equipped)
²High beam indicator
²Low fuel (premium cluster only)
²Low oil pressure
²Malfunction indicator (service engine soon) lamp
²Right and left turn signals
²Seat belt warning
²Security system
²Trac-Off (ABS equipped vehicles only)
The instrument cluster has a Vacuum Fluorescent
(VF) display for the following systems:
²Cruise
²Door (ajar)
²Odometer
²Set (cruise)
²Trac
²Trip
DIAGNOSIS AND TESTING
AIRBAG WARNING SYSTEM
For testing of this system refer to Group 8M, Pas-
sive Restraint Systems.
BRAKE SYSTEM WARNING LAMP TEST
The brake warning lamp illuminates when the
parking brake is applied with ignition switch turned
to the ON position. The same lamp will also illumi-
nate if one of the two service brake systems fail the
when brake pedal is applied.
To test the system:
²As the ignition switch is turned to the start posi-
tion the lamp should light.
²Turn ignition switch to the ON position and
apply the parking brake. The lamp should light.
If lamp fails to light inspect for:
²A burned out lamp
²Loose, corroded or damaged socket
²A damaged circuit board
²A broken or disconnected wire at the switch
²Defective switch
To test the service brake warning system, refer to
Group 5, Brakes, Hydraulic System Control Valves.
INSTRUMENT CLUSTER LAMPS
Every time the vehicle is switched to the START/
RUN position, the cluster goes through a BULB
CHECK. This tests most of the indicator lamps and
Vacuum Fluorescent (VF) displays. If only one lamp
is out, remove the instrument cluster and replace the
defective bulb or Light Emitting Diode (LED). If
some or all of the lamps fail to light, refer to the
proper Body Diagnostics Procedures Manual.
8E - 2 INSTRUMENT PANEL SYSTEMSPL

SPEED CONTROL SERVO-PCM OUTPUT
DESCRIPTION
The servo unit consists of a solenoid valve body,
and a vacuum chamber. The solenoid valve body con-
tains three solenoids:
²Vacuum
²Vent
²Dump
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's 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
at 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 duty cycles the vacuum and vent sole-
noids to maintain the set speed, or to accelerate and
decelerate 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. When
the brake is released, if vehicle speed exceeds 25
mph to resume, 30 mph to set, and the RES/ACCEL
switch has been depressed, ground for the vent and
vacuum circuits is restored.
SPEED CONTROL SWITCHESÐPCM INPUT
Description
There are two separate switch pods that operate
the speed control system. The steering-wheel-
mounted switches use multiplexed circuits to provide
inputs to the PCM for ON, OFF, RESUME, ACCEL-
ERATE, SET, DECEL and CANCEL modes. Refer tothe owner's manual for more information on speed
control switch functions and setting procedures.
The individual switches cannot be repaired. If one
switch fails, the entire switch module must be
replaced.
Operation
When speed control is selected by depressing the
ON, OFF switch, the PCM allows a set speed to be
stored in RAM for speed control. To store a set speed,
depress the SET switch while the vehicle is moving
at a speed between 25 and 85 mph. In order for the
speed control to engage, the brakes cannot be
applied, nor can the gear selector be indicating the
transmission is in Park or Neutral.
Once the speed control has been disengaged,
depressing the ACCEL switch restores the vehicle to
the target speed that was stored in the PCM's RAM.
NOTE: Depressing the OFF switch will erase the
set speed stored in the PCM's RAM.
If, while the speed control is engaged, the driver
wishes to increase vehicle speed, the PCM is pro-
grammed for an acceleration feature. With the
ACCEL switch held closed, the vehicle accelerates
slowly to the desired speed. The new target speed is
stored in the RAM when the ACCEL switch is
released. The PCM also has a ªtap-upº feature in
which vehicle speed increases at a rate of approxi-
mately 2 mph for each momentary switch activation
of the ACCEL switch.
The PCM also provides a means to decelerate with-
out disengaging speed control. To decelerate from an
existing recorded target speed, depress and hold the
COAST switch until the desired speed is reached.
Then release the switch. The ON, OFF switch oper-
ates two components: the PCM's ON, OFF input, and
the battery voltage to the brake switch, which powers
the speed control servo.
Multiplexing
The PCM sends out 5 volts through a fixed resistor
and monitors the voltage change between the fixed
resistor and the switches. If none of the switches are
depressed, the PCM will measure 5 volts at the sen-
sor point (open circuit). If a switch with no resistor is
closed, the PCM will measure 0 volts (grounded cir-
cuit). Now, if a resistor is added to a switch, then the
PCM will measure some voltage proportional to the
size of the resistor. By adding a different resistor to
each switch, the PCM will see a different voltage
depending on which switch is pushed.
8H - 2 VEHICLE SPEED CONTROL SYSTEMPL
DESCRIPTION AND OPERATION (Continued)