1993 CHEVROLET PLYMOUTH ACCLAIM ignition

In addition, there is an air regeneration cycle that
is controlled by the Control Module (CM). If the
height sensor signal is in the neutral or high posi-
tion. When the ignition switch is turned to the ON
position, after a 22 to 28 second delay, the compres-
sor will run from 2 to 6 seconds. To prevent excessive cycling between the compres-
sor and the exhaust solenoid circuits during normal
ride conditions. A 12 to 18 second delay is incorpo-
rated in the microprocessor.
HEIGHT SENSOR
A magnetic switch type sensor, located in the right
air shock absorber, monitors rear vehicle height. The
sensor sends signals to the (CM) relating to vehicle
rear suspension status (low, trim, high).
AIR LINES AND FITTINGS
To release an air supply line from a rear shock ab-
sorber assembly. Push in (toward shock absorber) on
the plastic ring of the shock absorber air line fitting.
Then while holding in the plastic ring on shock ab-
sorber fitting pull the air supply line strait out of fit-
ting (Fig. 3). The fitting has a unique push-in feature. A brass
type collet locks the air line in place. One rubber
O-ring seals the air line to prevent air leakage. To
attach air line, push into fitting (Fig. 4).
COMPRESSOR RELAY
The relay is mounted to a bracket on the Control
Module (CM). When the relay is energized, it allows
the compressor to operate. This unit is controlled by
the CM.
AIR ADJUSTABLE SHOCK ABSORBERS
Air shock absorbers are essentially hydraulic shock
absorbers with a neoprene bladder sealing upper and
lower sections together. This creates an air cylinder
inside of the shock absorber.
AIR DRYER
The air dryer is attached to the compressor. This
component serves two purposes; it absorbs moisture
from the atmosphere before it enters the system. And
with the internal valves maintains a residual system
pressure of 69 to 152 kPa (10 to 22 psi).
AIR CHECK, RESIDUAL (FIG. 5).
The air dryer has a valves arrangement that main-
tains 69 to 152 kPa (10 to 22 psi) in the air shocks.
This is to improve the ride characteristics of the ve-
hicle under light load conditions. To test this func-
tion, perform the following procedure: (1) Remove the air line from the dryer and right
shock absorber. Attach a piece of bulk nylon tubing
to one side of a Pressure Gauge (0-300 psi), and to
the right shock absorber (Fig. 5). (2) Attach another piece of nylon tubing from the
dryer (compressor) to other side of the pressure
gauge.
Fig. 2 Compressor AssemblyFig. 3 Release Air Line from Fitting
Fig. 4 Push Air Line into Fitting
2 - 60 SUSPENSION AND DRIVESHAFTS Ä

A compression ball sleeve nut and sleeve for 3/16
inch tubing with ball sleeve connector and an inter-
nal pipe T-fitting. Can be used to attach the tubing
to the pressure gauge. (3) Cycle ignition from OFF to ON.
(4) Apply a load to the rear of the vehicle (two as-
sistants or approximately 300-325 lbs.) to run com-
pressor and raise the vehicle. (5) Remove the load applied in Step 4. Allow the
system to exhaust and lower the vehicle. (6) When no more air can be exhausted, the gauge
should indicate 69 to 152 kPa (10 to 22 psi). (7) Remove the pressure gauge and nylon tubing.
Attach the air line between the dryer and shock ab-
sorber. Repeat Steps 3, 4, and 5 to ensure system air
pressure is in the shocks.
LEAK CHECKS
(1) Repeat Residual Air Check Steps 1, 2, 3, and 4.
Allow the system to fill until gauge reads 483 to 621
kPa (70 to 90 psi). If compressor is permitted to run until it reaches
its maximum output pressure, the vent solenoid
valve will function as a relief valve. The resulting
leak down, when compressor shuts off, will indicate a
false air leak. (2) With load still applied, disconnect wire harness
connector from the control module, then remove ap-
plied load. Vehicle should rise. Cycle ignition switch
to OFF. (3) Observe if pressure leaks down or holds steady
(wait approximately 15 minutes). (A) If system will not inflate beyond 345 kPa (50
psi). A severe leak may be indicated. Check for a
pinched pressure line between compressor and
shocks. (B) The standard soap solution check procedure is
acceptable. (C) If pressure holds steady, perform the diagnosis
procedures.
SYSTEM OPERATION
RAISING VEHICLE HEIGHT
When weight is added to the rear suspension. The
body of the vehicle is lowered, moving the height
sensor down. This action will activate the internal time delay
circuit. After a time delay of 12 to 18 seconds. The
control module (CM) activates the ground circuit to
the compressor relay. With the relay energized, the compressor motor
runs and air is sent through the system. As the
shock absorbers inflate, the body moves upward to a
corrected position. When the body reaches the correct
height, the control module (CM) stops the compressor
operation.
LOWERING VEHICLE HEIGHT
When the weight is removed from the vehicle. The
body moves upward, which allows the height sensor
to move upward and activate the internal time delay
circuit. After a time delay of 12 to 18 seconds. The (CM)
activates the exhaust solenoid circuit. Air is ex-
hausted from the shock absorbers through the air
dryer and exhaust solenoid to the atmosphere. As the body lowers, the height sensor is lowered to-
ward its original position. When the body reaches the
original vehicle height, the (CM) opens the exhaust
solenoid valve circuit.
COMPRESSOR PERFORMANCE TEST
This test can be performed on the vehicle. It is
used to evaluate compressor current draw, pressure
output, and leak down. (1) Disconnect the compressor motor wiring har-
ness connector. (2) Disconnect air line between dryer and right
shock absorber. (3) Connect an air pressure gauge into the system
(Fig. 5). (4) Connect an ammeter in series between the red
wire terminal on compressor connector and a 12 volt
power source. Also, connect a ground wire from the
black wire terminal on the compressor connector to a
good ground on the frame (Fig. 6). (5) If the current draw to the compressor motor ex-
ceeds 21 amperes, replace the compressor assembly. (6) When the air pressure stabilizes at 827 kPa
(120 psi), disconnect the (+) wire lead from the con-
nector. Replace the compressor assembly if any of the
following conditions exists:
Fig. 5 Pressure Gauge Installed in System
Ä SUSPENSION AND DRIVESHAFTS 2 - 61

REAR LEVELING DIAGNOSTIC PROCEDURES
SELF-DIAGNOSTICS
A self-diagnostic procedure is available for the ser-
vice technician to use to detect system malfunctions.
BEFORE DIAGNOSTICS TEST
Check the 20 amp fuse (position W40) and the 30
amp circuit breaker (position W5) to be assured they
are functional components. Check all connectors that link the system into the
main body wiring harness. These include compressor,
height sensor, control module, (Fig. 7) and relay.
Also check the underbody to in trunk and leveling
harness to main body harness connectors. Also, check
all air lines, connectors, and other components for
correct installation.
TEST LAMP PIN OPERATION
The monitor lamp pin output will be activated (test
lamp on) if the detection of abnormal system opera-
tion is determined by the CM.
AFTER COMPLETION OF REPAIRS
To initiate diagnostics, disconnect the test ground
wire then reconnect for repair verification.
TERMINATION OF SELF-DIAGNOSTICS
The self-diagnostic operation is terminated when
any of the following takes place:
² Disconnecting the diagnostic input from the
ground circuit.
² Turn the ignition switch to the off position.
When the self-diagnostic operation is terminated.
The control module resumes normal operation unless
it ceases operation. Due to it detecting a system mal-
function.
TEST WEIGHT
Weight between 275-300 lbs. must be added to rear
of vehicle before diagnostic testing begins.
DIAGNOSTICS (TO START PROCESS)
(1) Remove protective connector cover from diag-
nostic connector. (2) Insert wire into diagnostic ground pin. Then at-
tach to compressor ground pin, or as an alternate, in-
sert wire into diagnostic ground pin. Then ground
other end of test wire to body structure or a control
module fastener.
IGNITION
The following self diagnostic operation is initiated
by connecting the diagnostic ground pin to ground af-
ter ignition switch is turned ON. A monitor lamp
must be connected between the Test Lamp Ground
Pin and the Test Lamp Feed Pin to display the con-
trol module diagnostics status. See (Fig. 8) for diag-
nostic test pin locations.
OPERATION
(1) The compressor relay output. From the control
module (CM), is activated until the vehicle is in the
high position. The maximum relay output operation
time is 150 610 seconds. If the expected position is
not obtained, the CM ceases self-diagnostics and any
further operation. (I.e. neither operates the compres-
sor relay or exhaust outputs). The monitor lamp out-
put is continuously activated until ignition is cycled
from OFF to ON or 60 61 minutes has elapsed after
ignition was turned off. See Diagnostics Chart 1. (2) The monitor lamp output should flash to indi-
cate the position of the height sensor. The sensor
should be in the high position. A continuously
lighted monitor lamp will indicate a system failure.
Such as the compressor relay output has operated for
150 610 seconds but the height sensor did not move
to the high position within the right shock absorber).
See Diagnostic Chart 1. (3) Next the exhaust solenoid output is activated
until the vehicle is in the low position. The maxi-
mum exhaust solenoid operation time is 120 610 sec-
onds. If the expected position is not obtained, the
module ceases self-diagnostics and any further oper-
ation. The monitor lamp output is lighted continu-
ously until ignition is cycled from OFF to ON or 60
6 1 minutes has elapsed after ignition is turned off.
See Diagnostic Chart 4. (4) The monitor lamp should flash to indicate the
height sensor is in the low position. A continuouslyFig. 7 Control Module Connector
Fig. 8 Diagnostic Test Pin Location
Ä SUSPENSION AND DRIVESHAFTS 2 - 65

lighted monitor lamp will indicate a system failure.
Such as the exhaust solenoid operated for 120 610
seconds but the height sensor did not move to the
low position. See Diagnostic Chart 4. (5) The compressor relay output is activated to re-
turn the vehicle to the neutral (leveled) position. The
maximum operation time of the relay output is 150
6 10 seconds. If the expected position is not obtained.
The control module ceases self-diagnostics and any
further operation. The monitor lamp is continuously
lighted until the ignition is cycled from OFF to ON
or 60 61 minutes has elapsed after ignition is turned
off. The sensor will move to the neutral position. If not,
a continuously lighted monitor lamp will indicate a system failure. Such as the compressor relay output
operated for 150 610 seconds but the sensor did not
move to or sense the neutral position. See Diagnostic
Chart 1. (6) Completion of diagnostics, is when self diagnostic
procedure is successfully completed and control module
resumes normal operation. The diagnostic test is now
complete. Throughout the testing the vehicle load must
be maintained at a specific level. No loads are allowed
to be added/removed to/from the vehicle once the self
diagnosis tests have been initiated. The Diagnostic connector cover must be in-
stalled after completion of the test.
2 - 66 SUSPENSION AND DRIVESHAFTS Ä

(3) Check solenoid to volume canister joint.
² Front strut to solenoid valve connection.
² Rear spring to solenoid valve connection.
(4) Check air line for ruptures, cuts, splits or heat
damage. Use a soap and water solution or a liquid de-
veloped for leak detection.
SYSTEM OPERATION
ENGINE RUN OPERATION
The system will compensate for load
addition/removal when.
² The trunk and all doors are closed.
² The engine speed exceeds 600 R.P.M.
² Throttle angle is less than 65 degrees.
² The brake is not applied.
² You are not cornering above 10 mph.
² There is not a charging system problem with the
vehicle.
ENGINE OFF OPERATION
After passengers/load is removed from the vehicle
the system will correct the vehicle attitude after:
² The trunk and all doors are closed.
² The ignition switch is in the OFF position.
Opening the a door or trunk wakes up the body
computer and the air suspension module. The air
suspension system is now capable of leveling, if
required.
LONG TERM IGNITION OFF OPERATION
The system is capable of one an additional leveling
cycle. After 2 continuous hours of ignition key off and
no door open or trunk open activities. This feature is
implemented to eliminate possible ice freeze-up be-
tween the tire and the inner fender shield.
SYSTEM OPERATION INHIBITORS
The air suspension system is inhibited when:
² The trunk is open.
² A door(s) is/are open.
² The brake pedal is engaged.
² The throttle is at the wide open position.
² The charging system fails.
The maximum compressor pump or exhaust
time is 3 minutes.
SYSTEM FAILURES
Vehicles equipped with air suspension and overhead
console. Will alert the driver of an air suspension
system malfunction. A warning Check Air Suspension
will appear on the overhead console screen.
SAFETY CONCERNS
WARNING: REAR AIR SPRINGS MUST BE DEFLATED
BEFORE BEING REMOVED FROM THE VEHICLE.
WARNING: OPEN TRUNK, OR DOOR(S) OR REMOVE
GROUND STRAP FROM BATTERY BEFORE HOIST-
ING OR JACKING A VEHICLE DURING MECHANICAL
REPAIRS.
WARNING: IF THE VEHICLE NEEDS SERVICE OR
REPAIR OF THE REAR SHOCK ABSORBERS OR
REAR AXLE PIVOT BUSHINGS. THE REAR AIR
SPRINGS MUST HAVE THE AIR PRESSURE RE-
MOVED BEFORE THE VEHICLE CAN BE SERVICED
SAFELY.
SHIPPING MODE
(1) Removing shipping height signal for customer
use.
² Use DRB II tester and 1991 Chassis (Air Suspen-
sion) service cartridge.
² Follow DRB II requirements to cancel shipping
height message in the body computer.
² Connect the Ignition Off Draw (I.O.D.) circuit.
The connection of the IOD circuit will cancel
the Shipping height signal. (2) Return to shipping height.
² Set shipping command in the body computer using
the DRB II and the 1991 Chassis (Air suspension)
service cartridge.
² Disconnect the I.O.D. connector.
DIAGNOSIS
INITIAL DIAGNOSTIC CHECK
(1) Check for blown or missing fuses.
Fig. 9 Compressor Current Draw Test
2 - 78 SUSPENSION AND DRIVESHAFTS Ä

(2) Check all connectors for correct assembly. Check
all connectors for incorrectly installed termi-
nals. (3) Check pin #21 for minimum of 9.5 volts.
(4) Check pin #20 for minimum of 9.5 volts (with
ignition key on). (5) Check voltage at pins #5 and #16. The measure-
ment should exceed 0 volts. (6) Check pin #19 for continuity.
(7) The engine speed should exceed 680 rpm during
idle. All doors and trunk must be closed for the
system to function.
DIAGNOSTICS PROCEDURES
(1) Use the D.R.B. II tester and the 1991 air suspen-
sion diagnostic service cartridge to begin the trouble-
shooting process. (2) Use the D.R.B. mating connector under the dash
(drivers side) to plug-in the D.R.B. II test connector
(Fig. 10). (3) The tester will conduct a complete check of the
suspension system status. (4) The tester will list the steps to follow to access
and diagnose the failure. (5) A Volt/Ohm meter can be used for some diagnos-
tic testing.
HEIGHT SENSOR CHECK
If a sensor signal/signals are missing. Follow the
repair procedure listed below. (1) Check ground circuit continuity. (Remember
front and rear grounds are on different circuits. (2) For front ground circuit continuity check circuit
S 33. (3) For rear ground circuit continuity check circuit
X20. (4) Refer to control module pin out chart and wiring
diagram (see Group 8F in wiring diagram manual) for
individual circuit details. (5) If open circuits are not found replace the compo-
nent. Complete circuit testing and connector assem-
blies before replacing a strut or right rear shock. (6) To measure resistance values, see Height Sensor
Logic Chart and Initial Diagnostic Check in System
Operation.
HEIGHT SENSOR LOGIC CHART
Ä SUSPENSION AND DRIVESHAFTS 2 - 79

SERVICE ADJUSTMENTS INDEX
page page
Adjusting Rear Service Brakes ............... 4
Bleeding Brake System ..................... 6
Brake Hose and Tubing ................... 11
Master Cylinder Fluid Level .................. 4 Stop Lamp Switch Adjustment (All Vehicles)
.... 13
Test for Fluid Contamination ................. 7
Testing Application Adjuster Operation ......... 6
Wheel Stud Nut Tightening .................. 7
MASTER CYLINDER FLUID LEVEL
ALL EXCEPT AC/AY BODY WITH ABS
Check master cylinder reservoir brake fluid level a
minimum of twice a year. Master cylinder reservoirs are marked with the
words fill to bottom of rings indicating proper fluid
level (Fig. 1). If necessary, add fluid to bring the level to the bot-
tom of the primary reservoir split ring. Use only Mopar tbrake fluid or an equivalent from
a sealed container. Brake fluid must conform to DOT
3, specifications. DO NOT use brake fluid with a lower boiling
point, as brake failure could result during prolonged
hard braking. Use only brake fluid that was stored in a tightly-
sealed container. DO NOT use petroleum-based fluid because seal
damage in the brake system will result.
AC AND AY BODY WITH ANTI-LOCK BRAKES
The hydraulic assembly is equipped with a plastic
fluid reservoir with a filter/strainer in the filler neck
of the reservoir. The Anti-Lock brake system requires that the hy-
draulic accumulator be de-pressurized whenever
checking the brake fluid level. To check the brake
fluid level, the following procedure should be used: (1) With the ignition switch turned to the off position
and key removed. De-pressurize hydraulic accumula-
tor by applying brake pedal approximately 40 times,
using a pedal force of approximately 220 N (50 lbs.). A
noticeable change in pedal feel will occur when accu-
mulator is de-pressurized. Continue to apply brake
pedal several times after this change in pedal feel
occurs to insure that brake system is fully de-
pressurized. (2) Thoroughly clean both reservoir caps and sur-
rounding area of reservoir, (Fig. 2) before removing
caps. This is to avoid getting dirt into the reservoir and
contaminating the brake fluid. (3) Inspect the brake fluid to see if it is at the proper
level, see instructions on top of reservoir. (FILL TO
TOP OF WHITE SCREEN ON FRONT
FILTER/STRAINER.) (4) Fill reservoir with brake fluid to top of screen
(Fig. 3) on the filter/strainer located in brake fluid
reservoir. Only use brake fluid conforming to DOT 3
specifications such as Mopar tor equivalent.
(5) Replace brake fluid reservoir caps.
ADJUSTING REAR SERVICE BRAKES
Normally, self adjusting drum brakes will not
require manual brake shoe adjustment. Al-
though in the event of a brake reline it is advis-
able to make the initial adjustment manually to
speed up the adjusting time. (1) Raise the vehicle so all wheels are free to turn.
See Hoisting Recommendations in the Lubrication And
Maintenance Section, at the front of this service
manual. (2) Remove rear brake adjusting hole rubber plug
(Fig. 4), from the rear brake shoe support plate. (3) Be sure parking brake lever is fully re-
leased. Then back off parking brake cable adjust-
ment so there is slack in the cable. (4) Insert Brake Adjuster, Special Tool C-3784, (Fig.
5) or equivalent through the adjusting hole in support
plate and against star wheel of adjusting screw. Move
handle of tool upward until a slight drag is felt when
the road wheel is rotated. (5) Insert a thin screwdriver or piece of welding rod
into brake adjusting hole (Fig. 5). Push adjusting lever
out of engagement with star wheel. Care
Fig. 1 Master Cylinder Fluid Level (All Except AC/AY
Body W/ABS)
5 - 4 BRAKES Ä

HYDRAULIC SYSTEM CONTROL VALVES INDEX
page page
ABS Brake Proportioning Valve Operation ...... 27
General Information ....................... 26
Hydraulic System Service Procedures ......... 27 Non-ABS Proportioning Unit Operation
........ 26
Pressure Differential Warning Light Switch ...... 26
Testing ABS Proportioning Valves ............ 29
GENERAL INFORMATION
Most models not equipped with an Anti-Lock brak-
ing system have a combination hydraulic system con-
trol valve in the brake hydraulic system (Fig. 1). The
valve is attached to the frame rail below the master
cylinder.
The control valve assembly combines a warning
switch with a dual proportioning valve (Fig. 2) Proportioning valves balance front to rear braking
by controlling at a given ratio, the increase in rear
system hydraulic pressure above a preset level. Un-
der light pedal application, the valve allows full hy-
draulic pressure to the rear brakes. There is only one valve assembly in each vehicle,
see Valve Application Chart. During any service pro-
cedures identify valve assemblies by part number as
well as split point (PSI) and slope.
PRESSURE DIFFERENTIAL WARNING LIGHT
SWITCH
The hydraulic brake system, on non-ABS vehicles,
is split diagonally. The left front and right rear
brakes are part of one system. And the right front and left rear are part of another. Both systems are
routed through, but hydraulically separated by a Pres-
sure Differential Switch. The function of the Pressure
Differential Switch is to alert the driver of a malfunc-
tion in the brake system. If hydraulic pressure is lost in one system, the
warning light switch will activate a red light on the
instrument panel, when the brake pedal is depressed.
At this point the brakes require service. However, since
the brake systems are split diagonally the vehicle will
retain 50% of its stopping capability in the event of a
failure in either half. The warning light switch is the latching type. It
will automatically center itself after the repair is
made and the brake pedal is depressed. The instrument panel bulb can be checked each time
the ignition switch is turned to the start position or the
parking brake is set.
NON-ABS PROPORTIONING UNIT OPERATION
The proportioning valve section operates by trans-
mitting full input pressure to the rear brakes up to a
certain point. This is called the split point. Beyond this
point it reduces the amount of pressure increase to the
rear brakes according to a certain ratio. On light pedal applications equal brake pressure will
be transmitted to the front and rear brakes. On heavier
pedal applications the pressure transmitted
Fig. 1 Brake Combination Valve And Warning Switch Location
Fig. 2 Switch and Valve Assembly
5 - 26 BRAKES Ä