1988 JEEP CHEROKEE automatic transmission

with manifold pressure information.
Knock Sensor
The knock (detonation) sensor, located in the cylinder head,
provides an input signal to the ECU whenever detonation occurs. The
ECU then retards ignition advance to eliminate the detonation at the
applicable cylinders.
Speed Sensor
The speed sensor (or crankshaft position sensor) is mounted
at the flywheel/drive plate housing. The sensor detects the flywheel/
drive plate teeth as they pass during engine operation and sends an
electrical signal to the ECU, which calculates engine speed.
The flywheel/drive plate has a large trigger tooth and notch
located 90
and 12 small teeth before each top dead center (TDC)
position. When a small tooth or notch pass the magnetic core in the
sensor, the build-up and collapse of the magnetic field induces a
small voltage signal in the sensor pick-up windings.
The ECU counts these signals representing the number of teeth
as they pass the sensor. When a larger trigger tooth and notch pass
the magnetic core, a higher voltage signal is sent to the ECU. This
indicates to the ECU that a piston will be at the TDC position 12
teeth later. The ECU either advances or retards ignition timing as
necessary according to sensor inputs.
Battery Voltage
Battery voltage input to the ECU ensures that proper voltage
is applied to the injector. The ECU varies voltage to compensate for
battery voltage fluctuations.
Starter Motor Relay
The engine starter motor relay provides an input to the ECU,
indicating the starter motor is engaged.
Wide Open Throttle (WOT) Switch
The WOT switch is mounted on the side of the throttle body.
The switch provides a voltage signal to the ECU under wide open
throttle conditions. The ECU responds to this signal by enriching the
air/fuel mixture delivered to the injector.
Closed Throttle (Idle) Switch
This switch is integral with the idle speed actuator (ISA)
motor. The switch provides a voltage signal to the ECU, which
increases or decreases the throttle stop angle in response to engine
operating conditions.
Transmission Gear Position Indicator
The gear position indicator is mounted on vehicles equipped
with automatic transaxles. It provides a signal to the ECU to
indicate that the transaxle is in a driving mode and not in Park or
Neutral.
Power Steering Pressure Switch
The switch increases the idle speed during periods of high
power steering pump load and low engine RPM.
A/C Switch
The A/C switch sends a signal to the ECU when the air
conditioner is operating and when the compressor clutch must be
engaged to lower the temperature. The ECU, in turn, increases engine
speed to compensate for the added load of the air conditioner.
FUEL CONTROL

The ECU controls the A/C compressor clutch by means of the
A/C clutch relay. See Fig. 15.
UP-SHIFT INDICATOR LAMP
Manual transaxle vehicles are equipped with an up-shift
indicator lamp. The lamp is normally turned on when the ignition
switch is turned "ON", and is turned off when the engine starts.
The lamp will again light during engine operation, according
to engine speed and load conditions. A switch, located on the
transaxle, prevents lamp from lighting when transmission is shifted
to the next highest gear. If the shift of gears is not performed, the
ECU will turn the lamp off after 3-5 seconds.
MODES OF OPERATION
IGNITION SWITCH "ON" MODE
When the TBI system is activated by the ignition switch, the
system power relay is energized, and the fuel pump is energized by
the ECU through the fuel pump relay. The pump will operate for
approximately 1 second, unless the engine is operating or the starter
motor is engaged.
The ECU receives input from the CTS, MAT, and MAP sensors.
The up-shift indicator lamp is illuminated.
ENGINE START-UP MODE
When the starter motor is engaged, the ECU receives inputs
from the CTS and speed sensors, the starter motor relay, and the wide
open throttle switch. The fuel pump is activated by the ECU and
voltage is applied to the injector, with the ECU controlling
injection time.
The ECU determines proper ignition timing from the speed
sensor input. If the wide open throttle switch is engaged, the ECU
will deactivate the injector to prevent flooding.
ENGINE WARM-UP MODE
The ECU receives inputs from the CTS, MAT, MAP, speed, and
knock sensors. It also is informed of throttle, gear (automatic
transaxle models) and A/C control position.
The ECU provides a ground for the injector, precisely
controlling fuel delivery to the engine. The ECU also controls
ignition timing, engine idle speed and throttle stop angle. On
vehicles with manual transmissions, the up-shift indicator lamp is
controlled according to engine speed and load.
CRUISE MODE
During cruising speed, the ECU receives inputs from the CTS,
MAT, MAP, EGO, speed and knock sensors. It is also informed of
throttle, gear (automatic transaxle models), and A/C control position.\
The ECU provides a ground to the injector, precisely
controlling injector time. It also controls idle speed, throttle stop
angle, ignition timing, air/fuel mixture ratio and up-shift indicator
lamp.
DECELERATION MODE
During deceleration, the ECU receives inputs from the CTS,

ECU signal line and the other end connected to ground. As throttle
valve angle changes, a return voltage is sent back to the ECU through
the third wire. Output voltage to the ECU is about one volt when
throttle valve is at idle position, and about 5 volts when throttle
valve is at wide open throttle.
A dual TPS is used on automatic transmission equipped models.
The additional sensor provides throttle position information to the
transmission.
Knock Sensor
A knock sensor is mounted on the lower left side of block,
just above the oil pan. This sensor detects abnormal engine vibration
due to "detonation" and/or "pre-ignition". The knock sensor supplies
detonation information to the ECU. The ECU then alters ignition timing
as needed to maintain maximum timing under most operating conditions.
Park/Neutral (P/N) Switch
The P/N switch is mounted in automatic transmission equipped
vehicles. The switch indicates when the transmission is in Park or
Neutral.
Speed Sensor
The speed sensor is a nonadjustable sensor attached to the
flywheel/drive plate housing with special shoulder bolts. This sensor
provides Top Dead Center (TDC) and engine speed information to the ECU\
by counting the flywheel teeth as they pass during engine operation.
The flywheel has a large trigger tooth and notch located 12 small
teeth before each TDC position. See Fig. 2.
Fig. 2: Design of Speed Sensor
When a small tooth and notch pass the magnetic core of the
sensor, the concentration and collapse of the magnetic field created
induces a small voltage spike into the sensor pick-up coil windings.

AB BREVIA TIO NS

1988 J e ep C hero ke e
GENERAL INFORMATION
COMMONLY USED ABBREVIATION
"A" ABBREVIATION TABLE
"A" ABBREVIATION TABLE







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ABBREVIATION DEFINITION 










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A Amperes 

A/C Air Conditioning 

A/T Automatic Transmission/Transaxle 

AAP Auxiliary Accelerator Pump 

AB Air Bleed 

ABCV Air Bleed Control Valve 

ABDC After Bottom Dead Center 

ABRS Air Bag Restraint System 

ABS Anti-Lock Brake System 

AC Alternating Current 

ACC A/C Clutch Compressor 

ACCS A/C Cycling Switch 

ACCUM Accumulator 

ACCY Accessory 

ACT Air Charge Temperature Sensor 

ACV Thermactor Air Control Valve 

ADJ Adjust or Adjustable 

ADV Advance 

AFS Airflow Sensor 

AI Air Injection 

AIR or A.I.R. Air Injection Reactor 

AIS Air Injection System 

ALCL Assembly Line Communications Link 

ALDL Assembly Line Diagnostic Link 

ARC Automatic Ride Control 

ASCD Automatic Speed Control Device 

ASCS Air Suction Control Solenoid 

ASD Auto Shutdown 

ASDM Air Bag System Diagnostic Module 

ASV Air Suction Valve 

ATC Automatic Temperature Control 

ATDC After Top Dead Center 

ATF Automatic Transmission Fluid 

ATS Air Temperature Sensor 

AXOD Automatic Transaxle Overdrive 

Abs. Absolute 

Accy. Accessory 

Alt. Alternator or Altitude 

Amp. Ampere 

Assy. Assembly 

Auto. Automatic 

Aux. Auxiliary 

Avg. Average 











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"B" ABBREVIATION TABLE
"B" ABBREVIATION TABLE

of the scale, a symbol for defroster indicates defrost position. In
"BI-LEVEL" position, a mixture of floor heat and defroster air is
obtained.
The lower temperature control lever operates blend-air door
in heater core housing. At full right position, all air is directed
through heater core, providing maximum heat flow. At full left
position, all air is directed around heater core providing fresh air.
Control can be set in any intermediate position to provide a blend of
heated and unheated air. Heater must be in heat or defrost mode before
any air can enter vehicle.
TROUBLE SHOOTING
See JEEP TROUBLE SHOOTING at the end of this article.
REMOVAL & INSTALLATION
CONDENSER
Removal (Cherokee, Comanche & Wagoneer) NOTE: On these
models, condenser and receiver-drier are replaced
as a unit.
1) Drain radiator. Disconnect fan shroud and radiator hoses.
Disconnect automatic transmission cooler lines (if equipped).
Discharge A/C system using approved refrigerant recovery/recycling
equipment.
2) Disconnect A/C hoses from condenser. Unplug low pressure
switch. Remove radiator and condenser as an assembly. Detach condenser
retaining bolts. Separate condenser from radiator. Remove receiver-
drier from condenser.
NOTE: Plug receiver-drier openings whenever unit is removed from
condenser. Add 1 oz. of refrigerant oil (AMC No. 8132400) to
system when replacing condenser.
Installation
To install, reverse removal procedure. Fill radiator.
Evacuate, leak test, recharge and check A/C system operation.
Removal (Wrangler)
1) Discharge system (slowly to prevent loss of compressor
oil) using approved refrigerant recovery/recycling equipment. Drain
coolant. Remove fan shroud and radiator. Disconnect pressure line at
condenser. Remove condenser mounting screws. Tilt bottom of condenser
toward engine.
2) From underside of vehicle, disconnect hose attaching
receiver-drier to evaporator. Plug all openings to prevent entry of
dirt or moisture. Remove receiver-drier and condenser assembly. Remove
receiver-drier from condenser.
Installation
To install, reverse removal procedure. Fill radiator.
Evacuate, leak test, recharge and check A/C system operation.
RECEIVER-DRIER
NOTE: On Cherokee, Comanche and Wagoneer, receiver-drier is
removed with condenser and radiator as an assembly.
Removal (Wrangler)

\003
AU TO T R AN S D IA G NO SIS - A W 4

1988 J e ep C hero ke e
AUTOMATIC TRANSMISSIONS
Aisin Warner 4 Electronic Diagnosis
APPLICATION
NOTE: Transmission may also be referred to as AW-4.
TRANSMISSION APPLICATION









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Vehicle Application Transmission Model
Jeep
1987-96 Cherokee ................................... AW4
1987-92 Comanche ................................... AW4
1987 Grand Wagoneer ................................ AW4
1987-90 Wagoneer ................................... AW4
1992 Wrangler ...................................... AW4









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NOTE: Vehicle body code may be required when diagnosing or
repairing transmission, as body code may be used instead of
vehicle model name. See BODY CODE DESIGNATION table.
BODY CODE DESIGNATION









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Vehicle Model Body Code
Cherokee .............................................. XJ
Comanche .............................................. MJ
Grand Wagoneer ........................................ SJ
Wagoneer .............................................. XJ
Wrangler .............................................. YJ









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DESCRIPTION
The electronic control system for the AW-4 transmission
controls transmission shift points and torque converter lock-up.
Electronic control system consists of Transmission Control Module
(TCM), valve body solenoids, throttle position sensor, speed sensor,
neutral safety switch and brake switch.
NOTE: Transmission Control Module (TCM) may be referred to as
Transmission Control Unit (TCU). Neutral safety switch may
be referred to as park/neutral safety switch or gear select
switch.
OPERATION
TRANSMISSION CONTROL MODULE (TCM)
The TCM determines shift points and torque converter lock-up
based on input signals received from throttle position sensor, neutral
safety switch, speed sensor and brake switch. The TCM controls
transmission shift points and torque converter lock-up by operating
electric solenoids mounted on the valve body.
The TCM contains a self-diagnostic system used for
determining an electronic component failure. The TCM self-diagnostic

2) Connect the DRB-II to the transmission diagnostic
connector. See RETRIEVING FAULT CODES under SELF-DIAGNOSTIC SYSTEM for
diagnostic connector location.
CAUTION: If the vehicle is in 3rd or OD position and feels like it
is stuck in 3rd or jumping from 2-1 or 3-1, perform
TEST 10A - TESTING FOR INTERMITTENT SPEED SENSOR test below.
3) With the DRB-II, perform SYSTEM TEST. See SYSTEM TEST MODE
under DRB-II OPERATING MODES .
4) The DRB-II will instruct you to do some actions during the
System Test. The DRB-II will then look for the action to happen and
automatically go to the next test function. If you perform the
required action and the DRB-II does not move to the next function,
press ENTER. The DRB-II will continue the testing.
5) When the DRB-II states "VEHICLE DRIVE", the vehicle be
must be driven at a speed above 4 miles per hour to ensure accurate
testing of the vehicle speed sensor. Afterwards, the DRB-II will
display any fault codes that may be present.
6) When the system test is complete, if there are any fault
codes present, the DRB-II will automatically display the code(s).
7) There are two types of faults for the transmission
solenoids. They are displayed as "FAULT STORED" and "FAULT PRESENT".
Note that the tests are different in the chart below.
8) Perform the tests shown below in response to the indicated
fault codes.
NOTE: ALWAYS start diagnosis with the most recent code.
CODE-TO-TEST MENU
CODE-TO-TEST MENU







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Code:  Solenoid Affected:  Fault Status:  Perform: 








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None  None Affected  No Faults  Test 2A 








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700  Solenoid No. 1  Fault Present  Test 4A 








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700  Solenoid No. 1  Fault Stored  Test 3A 








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700  Solenoid No. 2  Fault Present  Test 4B 








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700  Solenoid No. 2  Fault Stored  Test 3A 








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700  Solenoid No. 3  Fault Present  Test 4C 








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700  Solenoid No. 3  Fault Stored  Test 3A 








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702  Speed Sensor Fault   Test 5A 








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703  Gear Select Fault   Test 6A 








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705  TPS Fault   Test 7A 








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708  Wrong TCU   Test 9A 











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TEST 2A - VERIFICATION TEST
NOTE: Perform TEST 1A - VERIFICATION OF THE COMPLAINT
before proceeding.

CO M PU TE R R ELE A R N P R O CED URES

1988 J e ep C hero ke e
GENERAL INFORMATION
Computer Relearn Procedures
All Models
* PLEASE READ THIS FIRST *
The following general procedures are to be used if
driveability problems are encountered after power loss or battery has
been disconnected. These procedures may provide an aid in eliminating
these problems.
To reduce the possibility of complaints, after any service
which requires battery power to be disconnected, vehicle should be
road tested.
COMPUTER RELEARN PROCEDURES
Vehicles equipped with engine or transmission computers may
require a relearn procedure after vehicle battery is disconnected.
Many vehicle computers memorize and store vehicle operation patterns
for optimum driveability and performance. When vehicle battery is
disconnected, this memory is lost. The computer will use default data
until new data from each key start is stored. As computer memorizes
vehicle operation for each new key start, driveability is restored.
Vehicle computers may memorize vehicles operation patterns for 40 of
more key starts.
Customers often complain of driveability problems during
relearn stage because vehicle acts differently then before being
serviced. Depending on type and make of vehicle and how it is
equipped, the following complaints (driveability problems) may exist:
* Harsh Or Poor Shift Quality
* Rough Or Unstable Idle
* Hesitation Or Stumble
* Rich Or Lean Running
* Poor Fuel Mileage
These symptoms and complaints should disappear after a number
of drive cycles have been memorized. To reduce the possibility of
complaints, after any service which requires battery power to be
disconnected, vehicle should be road tested. If a specific relearn
procedure is not available, the following procedure may be used:
Automatic Transmission
* Set parking brake, start engine in "P" or "N" position.
Warm-up vehicle to normal operating temperature or until
cooling fan cycles.
* Allow vehicle to idle for one minute in "N" position. Select
"D" and allow engine to idle for one minute.
* Accelerate at normal throttle position (20-50%) until vehicle
shifts into top gear.
* Cruise at light to medium throttle.
* Decelerate to a stop, allowing vehicle to downshift, and use
brakes normally.
* Process may be repeated as necessary.
Manual Transmission