2002 JEEP GRAND CHEROKEE Control

The high pressure relief valve vents only enough
refrigerant to reduce the system pressure, and then
re-seats itself. The majority of the refrigerant is con-
served in the system. If the valve vents refrigerant, it
does not mean that the valve is faulty.
The high pressure relief valve is a factory-cali-
brated unit. The valve cannot be adjusted or
repaired, and must not be removed or otherwise dis-
turbed. The valve is only serviced as a part of the
compressor assembly.
DIAGNOSIS AND TESTING - COMPRESSOR
NOISE
When investigating an air conditioning related
noise, you must first know the conditions under
which the noise occurs. These conditions include:
weather, vehicle speed, transmission in gear or neu-
tral, engine speed, engine temperature, and any
other special conditions. Noises that develop during
air conditioning operation can often be misleading.
For example: What sounds like a failed front bearing
or connecting rod, may be caused by loose bolts, nuts,
mounting brackets, or a loose compressor clutch
assembly.
Drive belts are speed sensitive. At different engine
speeds and depending upon belt tension, belts can
develop noises that are mistaken for a compressor
noise. Improper belt tension can cause a misleading
noise when the compressor clutch is engaged, which
may not occur when the compressor clutch is disen-
gaged. Check the serpentine drive belt condition and
tension as described in Cooling before beginning this
procedure.
(1) Select a quiet area for testing. Duplicate the
complaint conditions as much as possible. Switch the
compressor on and off several times to clearly iden-
tify the compressor noise. Listen to the compressor
while the clutch is engaged and disengaged. Probe
the compressor with an engine stethoscope or a long
screwdriver with the handle held to your ear to bet-
ter localize the source of the noise.
(2) Loosen all of the compressor mounting hard-
ware and retighten. Tighten the compressor clutch
mounting nut. Be certain that the clutch coil is
mounted securely to the compressor, and that the
clutch plate and pulley are properly aligned and have
the correct air gap. (Refer to 24 - HEATING & AIR
CONDITIONING/CONTROLS/A/C COMPRESSOR
CLUTCH - INSTALLATION)
(3) To duplicate a high-ambient temperature condi-
tion (high head pressure), restrict the air flow
through the condenser. Install a manifold gauge set
to be certain that the discharge pressure does not
exceed 2760 kPa (400 psi).
(4) Check the refrigerant system plumbing for
incorrect routing, rubbing or interference, which cancause unusual noises. Also check the refrigerant lines
for kinks or sharp bends that will restrict refrigerant
flow, which can cause noises. (Refer to 24 - HEAT-
ING & AIR CONDITIONING/PLUMBING - CAU-
TION - REFRIGERANT HOSES/LINES/TUBES
PRECAUTIONS)
(5) If the noise is from opening and closing of the
high pressure relief valve, reclaim, evacuate, and
recharge the refrigerant system. (Refer to 24 - HEAT-
ING & AIR CONDITIONING/PLUMBING - STAN-
DARD PROCEDURE - REFRIGERANT RECOVERY)
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - STANDARD PROCEDURE - REFRIG-
ERANT SYSTEM EVACUATE) (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE)If the high pressure relief valve still
does not seat properly, replace the a/c compressor.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING/A/C COMPRESSOR - REMOVAL)
(6) If the noise is from liquid slugging on the suc-
tion line, check the refrigerant oil level and the
refrigerant system charge. (Refer to 24 - HEATING
& AIR CONDITIONING/PLUMBING/REFRIGER-
ANT OIL - STANDARD PROCEDURE) (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
SPECIFICATIONS - CHARGE CAPACITY).
(7) If the noise continues, replace the compressor
and repeat Step 1.
REMOVAL
REMOVAL
The compressor may be removed and repositioned
without disconnecting the refrigerant lines or dis-
charging the refrigerant system. Discharging is not
necessary if servicing the compressor clutch or clutch
coil, the engine, the cylinder head, or the generator.
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
(1) Recover the refrigerant from the system. (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMB-
ING - STANDARD PROCEDURE - REFRIGERANT
RECOVERY)
(2) Disconnect and isolate the battery negative
cable.
(3) Remove the serpentine drive belt. Refer to
Cooling for the procedures.
(4) Unplug the compressor clutch coil wire harness
connector.
24 - 58 PLUMBINGWJ
A/C COMPRESSOR (Continued)

ING & AIR CONDITIONING/CONTROLS/A/C
PRESSURE TRANSDUCER - INSTALLATION).
(9) Evacuate the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE)
(10) Charge the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE)
(11) Connect the negative battery cable.
INSTALLATION
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
Any kinks or sharp bends in the refrigerant plumb-
ing will reduce the capacity of the entire air condi-
tioning system. Kinks and sharp bends reduce the
flow of refrigerant in the system. A good rule for the
flexible hose refrigerant lines is to keep the radius of
all bends at least ten times the diameter of the hose.
In addition, the flexible hose refrigerant lines should
be routed so they are at least 80 millimeters (3
inches) from the exhaust manifold.
High pressures are produced in the refrigerant sys-
tem when the air conditioning compressor is operat-
ing. Extreme care must be exercised to make sure
that each of the refrigerant system connections is
pressure-tight and leak free. It is a good practice to
inspect all flexible hose refrigerant lines at least once
a year to make sure they are in good condition and
properly routed.
(1) Remove the tape or plugs from the discharge
line block fitting and the manifold on the compressor.
Install the discharge line block fitting to the manifold
on the compressor. Tighten the mounting bolt to 25.4
N´m (225 in. lbs.).
(2) Remove the tape or plugs from the refrigerant
line fittings on the condenser inlet and the discharge
line. Connect the discharge line to the condenser
inlet. Tighten the retaining nut to 28 N´m (250 in.
lbs.).
(3) Install the a/c high pressure transducer(Refer
to 24 - HEATING & AIR CONDITIONING/CON-
TROLS/A/C PRESSURE TRANSDUCER - INSTAL-
LATION).
(4) Connect the battery negative cable.
(5) Evacuate the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM EVACUATE)(6) Charge the refrigerant system. (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
STANDARD PROCEDURE - REFRIGERANT SYS-
TEM CHARGE)
A/C EXPANSION VALVE
DESCRIPTION
The ªHº valve type thermal expansion valve (TXV)
is located at the front of the heater-A/C housing
between the liquid and suction lines and the evapo-
rator coil.
The expansion valve is a factory calibrated unit
and cannot be adjusted or repaired. If faulty or dam-
aged, the expansion valve must be replaced.
OPERATION
High-pressure, high temperature liquid refrigerant
from the liquid line passes through the expansion
valve orifice, converting it inot a low-pressure, low-
temperature mixture of liquid and gas before it
enters the evaporator coil. A temperature sensor in
the expansion valve control head monitors the tem-
perature of the refrigerant leaving the evaporator coil
throught the suction line, and adjusts the orifice size
at the liquid line to let the proper amoount of refrig-
erant into the evaporator coil to meet the vehicle
cooling requirements. Controlling the refrigerant flow
through the evaporator ensures that none of the
refrigerant leaving the evaporator is still in a liquid
state, which could damage the compressor.
DIAGNOSIS AND TESTING - A/C EXPANSION
VALVE
The expansion valve is located on the engine side
of the dash panel near the shock tower.
The expansion valve can fail in three different
positions (open, closed or restricted).
In an Open Position: this will result in a noisy
compressor or no cooling. The cause can be broken
spring, broken ball or excessive moisture in the A/C
system. If the spring or ball are found to be defective,
replace the expansion valve. If excessive moisture is
found in the A/C system, recycle the refrigerant.
In a Closed Position: There will be low suction
pressure and no cooling. This may be caused by a
failed power dome or excessive moisture in the A/C
system. If the power dome on the expansion valve is
found to be defective replace the expansion valve. If
excessive moisture is found recycle the refrigerant.
A Restricted Orifice: There will be low suction
pressure and no cooling. This may be caused by
debris in the refrigerant system. If debris is believed
to be the cause, recycle the refrigerant and replace
the expansion valve and the receiver/drier.
WJPLUMBING 24 - 65
A/C DISCHARGE LINE (Continued)

INSTALLATION
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
Any kinks or sharp bends in the refrigerant plumb-
ing will reduce the capacity of the entire air condi-
tioning system. Kinks and sharp bends reduce the
flow of refrigerant in the system. A good rule for the
flexible hose refrigerant lines is to keep the radius of
all bends at least ten times the diameter of the hose.
In addition, the flexible hose refrigerant lines should
be routed so they are at least 80 millimeters (3
inches) from the exhaust manifold.High pressures are produced in the refrigerant sys-
tem when the air conditioning compressor is operat-
ing. Extreme care must be exercised to make sure
that each of the refrigerant system connections is
pressure-tight and leak free. It is a good practice to
inspect all flexible hose refrigerant lines at least once
a year to make sure they are in good condition and
properly routed.
(1) Install the evaporator coil in the bottom half of
the HVAC housing. Be certain that the evaporator
foam insulator wrap is reinstalled.
(2) Reassemble the HVAC housing and install in
the vehicle. (Refer to 24 - HEATING & AIR CONDI-
TIONING/DISTRIBUTION/HVAC HOUSING -
ASSEMBLY) (Refer to 24 - HEATING & AIR CON-
DITIONING/DISTRIBUTION/HVAC HOUSING -
INSTALLATION)
NOTE: If the evaporator is replaced, add 60 millili-
ters (2 fluid ounces) of refrigerant oil to the refrig-
erant system.
Fig. 11 HVAC HOUSING- CASE SEPARATED
1 - ELECTRICIAL CONNECTORS
2 - VACUUM ACTUATOR
3 - RECIRCULATION DOOR
4 - THERMAL EXPANSION VALVE
5 - BLOWER MOTOR RESISTOR/CONTROLLER
6 - BLOWER WHEEL
7 - EVAPORATOR AND TUBES
8 - FIN SENSOR PROBE9 - BLEND DOOR
10 - PIVOT SHAFT (MOTOR REMOVED)
11 - PANEL/OUTLET DOOR
12 - LOWER HOUSING
13 - VACUUM ACTUATORS
14 - UPPER HOUSING
15 - VACUUM HARNESS
24 - 70 PLUMBINGWJ
A/C EVAPORATOR (Continued)

HEATER CORE
DESCRIPTION
The heater core is located in the HVAC housing,
under the instrument panel. It is a heat exchanger
made of rows of tubes and fins.
OPERATION
Engine coolant is circulated through heater hoses
to the heater core at all times. As the coolant flows
through the heater core, heat removed from the
engine is transferred to the heater core fins and
tubes. Air directed through the heater core picks up
the heat from the heater core fins. The temperature
control door allows control of the heater output air
temperature by controlling how much of the air flow-
ing through the HVAC housing is directed through
the heater core. The blower motor speed controls the
volume of air flowing through the HVAC housing.
The heater core cannot be repaired and, if faulty or
damaged, it must be replaced. Refer to Cooling for
more information on the engine cooling system, the
engine coolant and the heater hoses.
REMOVAL
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN AN ACCIDENTAL
AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
(1) Remove the HVAC housing from the vehicle.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - REMOVAL)
(2) Remove the foam gasket surrounding the core
tubes.
NOTE: Notice the orientation of the irregularly
shaped gasket on the tubes. The gasket must be
placed correctly to ensure proper sealing against
the body during reinstallation.(3)
Remove the screws and retainers that secure the
heater core and tubes to the HVAC housing (Fig. 12).
(4) Remove the mode door actuator if necessary,
for clearance to remove the core.
(5) Lift the heater core straight up and out of the
HVAC housing (Fig. 13).
(6) When replacing individual tubes, loosen and
remove the round tube-to-core clamp, and pull tube
from core.
INSTALLATION
WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS SECTION BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - WARNING) (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING - CAUTION)
Any kinks or sharp bends in the refrigerant plumb-
ing will reduce the capacity of the entire air condi-
tioning system. Kinks and sharp bends reduce the
flow of refrigerant in the system. A good rule for the
flexible hose refrigerant lines is to keep the radius of
all bends at least ten times the diameter of the hose.
In addition, the flexible hose refrigerant lines should
be routed so they are at least 80 millimeters (3
inches) from the exhaust manifold.
High pressures are produced in the refrigerant sys-
tem when the air conditioning compressor is operat-
ing. Extreme care must be exercised to make sure
that each of the refrigerant system connections is
Fig. 12 HEATER CORE, TUBES, AND RETAINERS
1 - TUBE-TO-CORE CLAMPS
2 - GROUND STRAP
3 - HVAC HOUSING
4 - TUBE RETAINERS AND SCREWS
5 - HEATER CORE
WJPLUMBING 24 - 71

pressure-tight and leak free. It is a good practice to
inspect all flexible hose refrigerant lines at least once
a year to make sure they are in good condition and
properly routed.
(1) When installing individual tubes, insert tube
into core ensuring that tube O-ring is seated in core
and not pinched. Hold tube in seated position while
installing the round tube-to-core clamp (Fig. 14).
NOTE: The round tube-to-heater-core clamp should
be left loose enough to turn the tube in the core.
Position the core in the housing, and then tighten
the tube-to-heater-core clamp after orienting the
tubes to the molded HVAC housing.
(2) Lower the heater core into the HVAC housing.
(3) Install the mode door actuator, if removed from
housing for core removal.
(4) Position the retainers over the heater core
tubes. Install and tighten the screws that secure the
heater core and retainers to the HVAC housing.
Tighten the screws to 2.2 N´m (20 in. lbs.).NOTE: The grounding strap is to be attached to the
lower heater core tube retainer.
(5) Reinstall the HVAC housing to the vehicle.
(Refer to 24 - HEATING & AIR CONDITIONING/
DISTRIBUTION/HVAC HOUSING - INSTALLA-
TION)
RECEIVER / DRIER
DESCRIPTION
The receiver/drier is mounted in the engine com-
partment between the condenser and is part of the
liquid line assembly. The filter/drier cannot be
repaired, if the filter/drier is faulty, damaged, left
open to the atmosphere or contaminated the line
assembly must be replaced.
OPERATION
The filter-drier performs a filtering action to pre-
vent foreign material in the refrigerant from contam-
inating the expansion valve. A desiccant bag is
mounted inside the filter-drier canister to absorb any
Fig. 13 HEATER CORE AND TUBES - (Typical)
1 - ELECTRICAL CONNECTORS
2 - EXPANSION VALVE
3 - ELECTRIC ACTUATOR
4 - OUTLET TO DEFROSTER DUCTS
5 - ELECTRIC ACTUATOR
6 - FLOOR DUCT
7 - TO REAR PASSENGER FLOOR AIR DUCTS8 - FLOOR DUCT
9 - HEATER CORE AND TUBES
10 - HOUSING DRAIN
11 - BLOWER MOTOR RESISTOR/CONTROLLER
12 - BLOWER MOTOR
13 - GROUND STRAP
24 - 72 PLUMBINGWJ
HEATER CORE (Continued)

VISCOUS HEATER
DESCRIPTION
DESCRIPTION
The diesel engine has an engine mounted mechan-
ical device called a Viscous Heater that is used to
heat the coolant coming from the engine to the
heater core. The Viscous Heater is driven by the
engine fan belt and has a electro-mechanical clutch
which is controlled by the HVAC control unit.
DESCRIPTION - VISCOUS HEATER CLUTCH
The basic viscous heater clutch assembly consists
of a stationary electromagnetic coil, a hub bearing
and pulley assembly and a clutch plate. The electro-
magnetic coil unit and the hub bearing and pulley
assembly are each retained on the nose of the com-
pressor front housing with snap rings (Fig. 17). The
clutch plate is keyed to the viscous heater shaft and
secured with a nut. These components provide the
means to engage and disengage the viscous heater
from the engine accessory drive belt.
OPERATION
OPERATION - VISCOUS HEATER
The Viscous Heater is driven by the engine fan
belt. The Viscous Heater has an electro-mechanical
clutch that receives a signal from the HVAC control
head and the Viscous Heater controller that ener-
gizes and engages the clutch. Once engaged theclutch allows the Viscous Heater to increase the tem-
perature of the coolant flowing to the heater core,
which provides heat the passenger compartment
quicker than normal engines without the Viscous
Heater. The Viscous Heater generates heat by means
of friction which heats a special Silicon Oil within its
housing which is then transferred to the engine cool-
ant when the coolant passes over fins within the
pump. Please note that the coolant is isolated from
the silicon oil within the pump housing. When
demand for passenger compartment heat decreases
the Viscous Heater clutch will receive an input from
the Viscous heater controller to disengage.
OPERATION - VISCOUS HEATER CLUTCH
When the clutch coil is energized, it magnetically
draws the clutch into contact with the pulley and
drives the viscous heater shaft. When the coil is not
energized the pulley freewheels on the clutch hub
bearing, which is part of the pulley. The viscous
heater clutch and coil are the only serviced parts on
the viscous heater assembly. If the viscous heater is
inoperative or damaged the entire assembly must be
replaced. The viscous heater clutch engagement is
controlled by several components: the viscous heater
controller, the engine powertrain control module and
the HVAC control head.
REMOVAL
REMOVAL - VISCOUS HEATER
(1) Drain the engine coolant(Refer to 7 - COOL-
ING/ENGINE - STANDARD PROCEDURE).
(2) Remove the engine accessory drive belt(Refer to
7 - COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL).
(3) Remove the heater hose clamps at the Viscous
Heater.
(4) Remove the heater hoses from the Viscous
Heater.
(5) Unplug the Viscous Heater clutch electrical
connector.
(6) Remove the bolts holding the Viscous Heater to
the mounting bracket.
(7) Remove the Viscous Heater from the vehicle.
REMOVAL - VISCOUS HEATER CLUTCH
(1) The viscous heater clutch can be serviced in
the vehicle and the cooling system does not have to
be drained.
(2) Disconnect and isolate the battery negative
cable.
(3) Remove the serpentine drive belt(Refer to 7 -
COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL).
Fig. 17 CLUTCH ASSEMBLY- typical
1 - CLUTCH PLATE
2 - SHAFT KEY
3 - PULLEY
4 - COIL
5 - CLUTCH SHIMS
6 - SNAP RING
7 - SNAP RING
24 - 76 PLUMBINGWJ

EMISSIONS CONTROL
TABLE OF CONTENTS
page page
EMISSIONS CONTROL
DESCRIPTION
DESCRIPTION - EMISSION CONTROL
SYSTEM.............................1
DESCRIPTION - STATE DISPLAY TEST
MODE...............................2
DESCRIPTION - CIRCUIT ACTUATION TEST
MODE...............................2
DESCRIPTION - DIAGNOSTIC TROUBLE
CODES..............................2DESCRIPTION - TASK MANAGER.........17
DESCRIPTION - MONITORED SYSTEMS . . . 17
DESCRIPTION - TRIP DEFINITION........19
DESCRIPTION - COMPONENT MONITORS . . 19
DESCRIPTION - NON-MONITORED
CIRCUITS...........................20
DESCRIPTION - HIGH AND LOW LIMITS . . . 20
DESCRIPTION - LOAD VALUE...........20
OPERATION - TASK MANAGER............21
EVAPORATIVE EMISSIONS................24
EMISSIONS CONTROL
DESCRIPTION
DESCRIPTION - EMISSION CONTROL SYSTEM
The Powertrain Control Module (PCM) monitors
many different circuits in the fuel injection, ignition,
emission and engine systems. If the PCM senses a prob-
lem with a monitored circuit often enough to indicate an
actual problem, it stores a Diagnostic Trouble Code
(DTC) in the PCM's memory. If the code applies to a
non-emissions related component or system, and the
problem is repaired or ceases to exist, the PCM cancels
the code after 40 warm-up cycles. Diagnostic trouble
codes that affect vehicle emissions illuminate the Mal-
function Indicator (check engine) Lamp. Refer to Mal-
function Indicator Lamp in this section.
Certain criteria must be met before the PCM
stores a DTC in memory. The criteria may be a spe-
cific range of engine RPM, engine temperature,
and/or input voltage to the PCM.
The PCM might not store a DTC for a monitored cir-
cuit even though a malfunction has occurred. This may
happen because one of the DTC criteria for the circuit
has not been met.For example
,assume the diagnostic
trouble code criteria requires the PCM to monitor the
circuit only when the engine operates between 750 and
2000 RPM. Suppose the sensor's output circuit shorts to
ground when engine operates above 2400 RPM (result-
ing in 0 volt input to the PCM). Because the condition
happens at an engine speed above the maximum thresh-
old (2000 rpm), the PCM will not store a DTC.
There are several operating conditions for which
the PCM monitors and sets DTC's. Refer to Moni-
tored Systems, Components, and Non-Monitored Cir-
cuits in this section.Technicians must retrieve stored DTC's by connect-
ing the DRB scan tool (or an equivalent scan tool) to
the 16±way data link connector (Fig. 1).
NOTE: Various diagnostic procedures may actually
cause a diagnostic monitor to set a DTC. For
instance, pulling a spark plug wire to perform a
spark test may set the misfire code. When a repair
is completed and verified, connect the DRB scan
tool to the 16±way data link connector to erase all
DTC's and extinguish the MIL (check engine lamp).Fig. 1 Data Link (Diagnostic) Connector Location
1 - INSTRUMENT PANEL LOWER/LEFT EDGE
2 - DATA LINK CONNECTOR
WJEMISSIONS CONTROL 25 - 1

DESCRIPTION - STATE DISPLAY TEST MODE
The switch inputs to the Powertrain Control Mod-
ule (PCM) have two recognized states; HIGH and
LOW. For this reason, the PCM cannot recognize the
difference between a selected switch position versus
an open circuit, a short circuit, or a defective switch.
If the State Display screen shows the change from
HIGH to LOW or LOW to HIGH, assume the entire
switch circuit to the PCM functions properly. Connect
the DRB scan tool to the data link connector and
access the state display screen. Then access either
State Display Inputs and Outputs or State Display
Sensors.
DESCRIPTION - CIRCUIT ACTUATION TEST
MODE
The Circuit Actuation Test Mode checks for proper
operation of output circuits or devices the Powertrain
Control Module (PCM) may not internally recognize.
The PCM attempts to activate these outputs and
allow an observer to verify proper operation. Most of
the tests provide an audible or visual indication of
device operation (click of relay contacts, fuel spray,
etc.). Except for intermittent conditions, if a device
functions properly during testing, assume the device,
its associated wiring, and driver circuit work cor-
rectly. Connect the DRB scan tool to the data link
connector and access the Actuators screen.
DESCRIPTION - DIAGNOSTIC TROUBLE CODES
A Diagnostic Trouble Code (DTC) indicates the
PCM has recognized an abnormal condition in the
system.Remember that DTC's are the results of a sys-
tem or circuit failure, but do not directly iden-
tify the failed component or components.
NOTE: For a list of DTC's, refer to the charts in this
section.
BULB CHECK
Each time the ignition key is turned to the ON
position, the malfunction indicator (check engine)
lamp on the instrument panel should illuminate for
approximately 2 seconds then go out. This is done for
a bulb check.
OBTAINING DTC'S USING DRB SCAN TOOL
(1) Connect the DRB scan tool to the data link
(diagnostic) connector. This connector is located in
the passenger compartment; at the lower edge of
instrument panel; near the steering column.
(2) Turn the ignition switch on and access the
ªRead Faultº screen.
(3) Record all the DTC's and ªfreeze frameº infor-
mation shown on the DRB scan tool.
(4) To erase DTC's, use the ªErase Trouble Codeº
data screen on the DRB scan tool.Do not erase any
DTC's until problems have been investigated
and repairs have been performed.
(M)Malfunction Indicator Lamp (MIL) illuminated during engine operation if this DTC was recorded
(depending if required by CARB and/or EPA). MIL is displayed as an engine icon on instrument panel.
(G)Generator lamp illuminated
Generic Scan
Tool P-CodeDRB Scan Tool Display Brief Description of DTC
P0030 (M) 1/1 O2 Sensor Heater Circuit
MalfunctionProblem detected in oxygen sensor heater relay circuit.
P0031 (M) 1/1 O2 Sensor Heater Circuit Low Problem detected in oxygen sensor heater relay circuit.
P0032 (M) 1/1 O2 Sensor Heater Circuit High Problem detected in oxygen sensor heater relay circuit.
P0036 (M) 1/2 O2 Sensor Heater Circuit
MalfunctionProblem detected in oxygen sensor heater relay circuit.
P0037 (M) 1/2 O2 Sensor Heater Circuit Low Problem detected in oxygen sensor heater relay circuit.
P0038 (M) 1/2 O2 Sensor Heater Circuit High Problem detected in oxygen sensor heater relay circuit.
P0043 (M) 1/3 O2 Sensor Heater Circuit Low Problem detected in oxygen sensor heater relay circuit.
P0044 (M) 1/3 O2 Sensor Heater Circuit High Problem detected in oxygen sensor heater relay circuit.
P0051 (M) 2/1 O2 Sensor Heater Circuit Low Problem detected in oxygen sensor heater relay circuit.
P0052 (M) 2/1 O2 Sensor Heater Circuit High Problem detected in oxygen sensor heater relay circuit.
25 - 2 EMISSIONS CONTROLWJ
EMISSIONS CONTROL (Continued)