1995 JEEP YJ ABS

(2) Align and attach harness connector to ECU.
Slide connector into engagement with tangs on ECU.
Then tilt connector downward and into engagement
with ECU pin terminals. Exercise care as pin termi-
nals can be damaged if connector is forced into place.
(3) Connect harness to security alarm module, if
equipped.
(4) Position ECU bracket under instrument panel.
(5) Install and tighten ECU mounting bracket
bolts/nuts to 8-14 Nzm (75- 125 in. lbs.) torque.
(6) Install trim panel on instrument panel, if re-
moved.
ECU REMOVAL/INSTALLATION (YJ MODELS)
The antilock ECU is attached to the dash panel in-
side the passenger compartment. It is positioned just
above the heater/air conditioning plenum housing, in
line with the glove box (Fig. 16).
The ECU is attached to the dash panel by bolts
and nuts that are accessible from the engine com-
partment. The fasteners are located just to the right
of the battery.
On models with air conditioning, it will be neces-
sary to remove the air conditioning fascia panel and
ducts for access to the ECU and harness connecter.
HCU REMOVAL (XJ)
A new design HCU is used in 1995 models. The
new HCU has built-in accumulators that store the
extra fluid released for antilock mode operation. As a
result, the master cylinder and HCU are no longer
interconnected by hoses.The 1995 and prior hy-
draulic control units are NOT interchangeable.
(1) Disconnect vent hoses at air cleaner cover.
(2) Loosen clamp securing air cleaner hose to in-
take manifold. Use screwdriver to tap clamp loose.
(3) Remove air cleaner cover and hose. Then re-
move air filter from air cleaner shell (Fig. 17).
(4) Remove two bolts and one nut that secure air
cleaner housing to body panel (Fig. 17).
(5) Remove air cleaner housing from engine com-
partment.
Fig. 16 ECU Location (YJ)
Fig. 17 Air Cleaner Components
JABS OPERATION AND SERVICE 5 - 41

(6) Disconnect both flex brakelines at HCU (Fig. 18).
(7) Disconnect HCU solenoid harness from main
harness (Fig. 19).
(8) Disconnect HCU pump motor harness (Fig. 20).(9) If HCU mounting bracket will be left in place,
it will be necessary to remove HCU solenoid harness
connecter from mounting bracket. Remove connecter
fasteners, by squeezing them closed with needle nose
pliers; then pulling them out of bracket.
(10) Disconnect lines to front/rear brakes at lower
left side of HCU (Fig. 21).
(11) Remove HCU as follows:
(a) If only the HCU will be removed, remove
three shoulder bolts attaching HCU to mounting
bracket and remove HCU (Fig. 22).
(b) If HCU and bracket will be removed as as-
sembly, remove three nuts attaching HCU to stud
plate and remove HCU and bracket as assembly.
Fig. 18 Disconnecting Flex Lines From HCU
Fig. 19 Disconnecting HCU Solenoid Harness
Fig. 20 Disconnecting HCU Pump Harness
Fig. 21 HCU Front/Rear Brakeline Connections
Fig. 22 HCU Assembly
5 - 42 ABS OPERATION AND SERVICEJ

HCU INSTALLATION (XJ)
(1) Install HCU as follows:
(a) If only the HCU was removed, position HCU
in mounting bracket. Then install and tighten
three shoulder bolts that attach HCU to bracket
(Figs. 23 and 24). One bolt is used at forward end
of bracket and two at rear as shown.
(b) If HCU and bracket were removed as assem-
bly, position bracket on studs and install attaching
nuts. Tighten nuts to 10-13 Nzm (92-112 in. lbs.)
torque.
(c) On right hand drive models, If brackets were
removed, assemble brackets. Then position lower
bracket on body studs and install attaching nuts
and the one attaching bolt (Fig. 25).
(2) If HCU mounting bracket was not removed,
press solenoid harness connecter fasteners into
mounting bracket.
(3) Connect HCU pump motor and solenoid har-
nesses (Figs. 19 and 20).
(4) Connect brakelines from front/rear brakes to
HCU. Start brakeline fittings in HCU ports by handto avoid cross threading (Fig. 26). Then tighten line
fittings snug but not to required torque at this time.
(5) Connect flex lines to HCU (Fig. 18). Start
brakeline fittings in flex line ports by hand to avoid
cross threading. Then tighten line fittings snug but
not to required torque at this time.
(6) Bleed brakes. Refer to procedure in Brake Flu-
id-Brake Bleeding-Brakelines And Hoses section.
(7) Tighten brakeline fittings to following torques
after brake bleeding: 15- 18 Nzm (130-160 in. lbs.) at
HCU and master cylinder and 18-24 Nzm (160-210 in.
lbs.) at combination valve.
(8) Install engine air cleaner assembly and hoses.
(9) Connect vacuum lines to manifold fittings.
(10) Check brake pedal action before moving vehi-
cle. Bleed brakes again if pedal is not firm (feels soft/
spongy).
Fig. 23 Installing HCU Front Shoulder Bolt
Fig. 24 Installing HCU Rear Shoulder Bolts
Fig. 25 HCU And Bracket Mounting (RHD Models)
Fig. 26 Starting Brakelines In HCU (By Hand)
JABS OPERATION AND SERVICE 5 - 43

HCU REMOVAL (YJ)
(1) Place shop towels under master cylinder and
HCU brakelines.
(2) Disconnect flex lines at upper part of HCU.
(3) Disconnect solenoid and pump harness wires at
HCU harness connecters.
(4) Disconnect lines to front/rear brakes at lower
part of HCU.
(5) Remove shoulder bolts attaching HCU to
mounting bracket and remove HCU.
HCU INSTALLATION (YJ)
(1) Position HCU in mounting bracket (Fig. 27).
(2) Install shoulder bolts that attach HCU to
bracket.
(3) Connect brakelines to HCU. Start brakeline fit-
tings by hand to avoid cross threading. Tighten fit-
tings snug but not to torque at this time.
(4) Connect HCU pump and solenoid harness wires
to engine compartment harness.
(5) Fill and bleed brake system.
(6) Tighten brakeline fittings to 15-18 Nzm
(130-160 in. lbs.) at HCU and master cylinder, and to
18-24 Nzm (160-210 in. lbs.) at combination valve.
Fig. 27 HCU Mounting (YJ)
5 - 44 ABS OPERATION AND SERVICEJ

PARKING BRAKE REAR CABLE REPLACEMENT (YJ)
(1) Raise vehicle and loosen equalizer nuts (Fig.
17).
(2) Remove clamp and cotter pin attaching rear ca-
ble to equalizer and remove cable.
(3) Remove cable clips.
(4) Remove rear wheel and brake drum.
(5) Remove secondary brakeshoe and disconnect
cable from lever on brakeshoe.
(6) Compress cable retainer with hose clamp (Fig.
16) and remove cable from backing plate.
(7) Install new cable in backing plate. Be sure ca-
ble retainer lock tabs are engaged in plate.
(8) Install secondary brakeshoe.
(9) Adjust brakeshoes to brake drum and install
drum and wheel.
(10) Install cable in equalizer. Secure cable with
retainer and cotter pin.
(11) Install cable clips.
(12) Adjust parking brakes. Refer to procedure in
this section.
PARKING BRAKE SWITCH
The parking brake switch is located on the lever
assembly on XJ models, or on the foot pedal assem-
bly on YJ models (Fig. 18). Switch replacement is de-
scribed in the parking brake lever or foot pedal
removal/installation procedures in this section.
Fig. 17 Parking Brake Components (YJ)
Fig. 18 Parking Brake Switch Location
5 - 68 PARKING BRAKESJ

COOLANT
GENERAL INFORMATION
The cooling system is designed around the coolant.
Coolant flows through the engine water jackets ab-
sorbing heat produced during engine operation. The
coolant carries heat to the radiator and heater core.
Here it is transferred to the ambient air passing
through the radiator and heater core fins. The cool-
ant also removes heat from the automatic transmis-
sion fluid in vehicles equipped with an automatic
transmission.
COOLANT PERFORMANCE
The required ethylene-glycol (antifreeze) and water
mixture depends upon climate and vehicle operating
conditions. The coolant performance of various mix-
tures follows:
Pure Water-Water can absorb more heat than a
mixture of water and ethylene-glycol. This is for pur-
pose of heat transfer only. Water also freezes at a
higher temperature and allows corrosion.
100 percent Ethylene-Glycol-The corrosion in-
hibiting additives in ethylene-glycol need the pres-
ence of water to dissolve. Without water, additives
form deposits in system. These act as insulation
causing temperature to rise to as high as 149ÉC
(300ÉF). This temperature is hot enough to melt plas-
tic and soften solder. The increased temperature can
result in engine detonation. In addition, 100 percent
ethylene-glycol freezes at -22ÉC (-8ÉF).
50/50 Ethylene-Glycol and Water-Is the recom-
mended mixture, it provides protection against freez-
ing to -37ÉC (-35ÉF). The antifreeze concentration
must alwaysbe a minimum of 44 percent, year-
round in all climates. If percentage is lower, engine
parts may be eroded by cavitation. Maximum protec-
tion against freezing is provided with a 68 percent
antifreeze concentration, which prevents freezing
down to -67.7ÉC (-90ÉF). A higher percentage will
freeze at a warmer temperature. Also, a higher per-
centage of antifreeze can cause the engine to over-
heat because specific heat of antifreeze is lower than
that of water.
CAUTION: Richer antifreeze mixtures cannot be
measured with normal field equipment and can
cause problems associated with 100 percent ethyl-
ene-glycol.
COOLANT SELECTION-ADDITIVES
Coolant should be maintained at the specified level
with a mixture of ethylene glycol-based antifreeze
and low mineral content water. Only use an anti-
freeze containing ALUGARD 340-2 Ÿ.CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
COOLANT SERVICE
It is recommended that the cooling system be
drained and flushed at 84,000 kilometers (52,500
miles), or 3 years, whichever occurs first. Then every
two years, or 48,000 kilometers (30,000 miles),
whichever occurs first.
COOLANT LEVEL CHECKÐROUTINE
Do not remove radiator cap for routine cool-
ant level inspections. The coolant level can be
checked at coolant reserve/overflow tank.
The coolant reserve/overflow system provides a
quick visual method for determining coolant level
without removing radiator pressure cap. With engine
idling and at normal operating temperature, observe
coolant level in reserve/overflow tank. The coolant
level should be between ADD and FULL marks.
ADDING ADDITIONAL COOLANTÐROUTINE
Do not remove radiator cap to add coolant to
system.When adding coolant to maintain correct
level, do so at coolant reserve/overflow tank. Use a
50/50 mixture of ethylene-glycol antifreeze containing
Alugard 340-2 Ÿ and low mineral content water. Re-
move radiator cap only for testing or when refilling
system after service. Removing cap unnecessarily can
cause loss of coolant and allow air to enter system,
which produces corrosion.
COOLANT LEVEL CHECK-SERVICE
The cooling system is closed and designed to main-
tain coolant level to top of radiator.
WARNING: DO NOT OPEN RADIATOR DRAINCOCK
WITH ENGINE RUNNING OR WHILE ENGINE IS HOT
AND COOLING SYSTEM IS UNDER PRESSURE.
When vehicle servicing requires a coolant level
check in radiator, drain several ounces of coolant
from radiator drain cock. Do this while observing
coolant reserve/overflow system tank. The coolant
level in reserve/overflow tank should drop slightly. If
not, inspect for a leak between radiator and coolant
reserve/overflow system connection. Remove radiator
cap. The coolant level should be to top of radiator. If
not and if coolant level in reserve/overflow tank is at
ADD mark, check for:
²An air leak in coolant reserve/overflow tank or its
hose
²An air leak in radiator filler neck
²Leak in pressure cap seal to radiator filler neck
LOW COOLANT LEVEL-AERATION
If the coolant level in radiator drops below top of
radiator core tubes, air will enter cooling system.
7 - 20 COOLING SYSTEM SERVICE PROCEDURESJ

WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING.
Carefully remove the radiator pressure cap from
the filler neck and check the coolant level. Push
down on the cap to disengage it from the stop tabs.
Wipe the inner part of the filler neck and examine
the lower inside sealing seat for nicks, cracks, paint,
dirt and solder residue. Inspect the reserve/overflow
tank tube for internal obstructions. Insert a wire
through the tube to be sure it is not obstructed.
Inspect the cams on the outside part of the filler
neck. If the cams are bent, seating of pressure cap
valve and tester seal will be affected. Replace cap if
cams are bent.
Attach pressure tester 7700 (or an equivalent) to
the radiator filler neck (Fig. 21).Operate the tester pump to apply 124 kPa (18 psi)
pressure to the system. If the hoses enlarge exces-
sively or bulge while testing, replace as necessary.
Observe the gauge pointer and determine the condi-
tion of the cooling system according to the following
criteria:
²Holds Steady: If the pointer remains steady for
two minutes, there are no serious coolant leaks in
the system. However, there could be an internal leak
that does not appear with normal system test pres-
sure. Inspect for interior leakage or do the Internal
Leakage Test. Do this if it is certain that coolant is
being lost and no leaks can be detected.
²Drops Slowly: Shows a small leak or seepage is oc-
curring. Examine all connections for seepage or slight
leakage with a flashlight. Inspect the radiator, hoses,
gasket edges and heater. Seal any small leak holes
with a Sealer Lubricant or equivalent. Repair leak
holes and reinspect the system with pressure ap-
plied.
²Drops Quickly: Shows that a serious leakage is oc-
curring. Examine the system for serious external
leakage. If no leaks are visible, inspect for internal
leakage. Large radiator leak holes should be repaired
by a reputable radiator repair shop.
INTERNAL LEAKAGE INSPECTION
Remove the engine oil pan drain plug and drain a
small amount of engine oil. Coolant, being heavier
than engine oil, will drain first. Another way of test-
ing is to operate the engine and check for water glob-
ules on the engine oil dipstick. Also inspect the
automatic transmission oil dipstick for water glob-
ules. Inspect the automatic transmission fluid cooler
for leakage. Operate the engine without the pressure
cap on the radiator until thermostat opens.
Attach a pressure tester to the filler neck. If pres-
sure builds up quickly, a leak exists as a result of a
faulty cylinder head gasket or crack in the engine.
Repair as necessary.
WARNING: DO NOT ALLOW PRESSURE TO EX-
CEED 124 KPA (18 PSI). TURN THE ENGINE OFF.
TO RELEASE THE PRESSURE, ROCK THE TESTER
FROM SIDE TO SIDE. WHEN REMOVING THE
TESTER, DO NOT TURN THE TESTER MORE THAN
1/2 TURN IF THE SYSTEM IS UNDER PRESSURE.
If there is no immediate pressure increase, pump
the pressure tester until the indicated pressure is
within the system range. Vibration of the gauge
pointer indicates compression or combustion leakage
into the cooling system.
WARNING: DO NOT DISCONNECT THE SPARK
PLUG WIRES WHILE THE ENGINE IS OPERATING.
Fig. 20 Leak Detection Using Black LightÐTypical
Fig. 21 Pressurizing SystemÐTypical
JCOOLING SYSTEM SERVICE PROCEDURES 7 - 23

CAUTION: Do not operate the engine with a spark
plug shorted for more than a minute. The catalytic
converter may be damaged.
Isolate the compression leak by shorting each
spark plug to the cylinder block. The gauge pointer
should stop or decrease vibration when spark plug
for leaking cylinder is shorted. This happens because
of the absence of combustion pressure.
COMBUSTION LEAKAGE TEST (WITHOUT
PRESSURE TESTER)
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
Drain sufficient coolant to allow for thermostat re-
moval. Refer to Thermostat Replacement. Disconnect
the water pump drive belt.
Disconnect the upper radiator hose from the ther-
mostat housing. Remove the housing and thermostat.
Install the thermostat housing.
Add coolant to the radiator to bring the level to
within 6.3 mm (1/4 in) of the top of the thermostat
housing.
CAUTION: Avoid overheating. Do not operate the
engine for an excessive period of time. Open the
draincock immediately after the test to eliminate
boil over of coolant.
Start the engine and accelerate rapidly three times
(to approximately 3000 rpm) while observing the
coolant. If internal engine combustion gases are leak-
ing into the cooling system, bubbles will appear in
the coolant. If bubbles do not appear, there is no in-
ternal combustion gas leakage.
COOLANT RESERVE/OVERFLOW SYSTEM
The system works along with the radiator pressure
cap. This is done by using thermal expansion and
contraction of the coolant to keep the coolant free of
trapped air. It provides:
²A volume for coolant expansion and contraction.
²A convenient and safe method for checking/adjust-
ing coolant level at atmospheric pressure. This is
done without removing the radiator pressure cap.
²Some reserve coolant to the radiator to cover mi-
nor leaks and evaporation or boiling losses.
As the engine cools, a vacuum is formed in the
cooling system of both the radiator and engine. Cool-ant will then be drawn from the coolant tank and re-
turned to a proper level in the radiator.
The coolant reserve/overflow system consists of a
radiator mounted pressurized cap, a plastic reserve/
overflow tank (Figs. 22, 23 or 24), a tube (hose) con-
necting the radiator and tank, and an overflow tube
on the side of the tank.
Fig. 22 Reserve/Overflow TankÐYJ Models
Fig. 23 Reserve/Overflow TankÐXJ ModelsÐExcept
Right Hand Drive
7 - 24 COOLING SYSTEM SERVICE PROCEDURESJ