2002 JEEP GRAND CHEROKEE pressure testing

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)

CCV HOSE
DIAGNOSIS AND TESTING - CCV SYSTEM -
4.0L
Before attempting diagnosis, be sure locations of
fixed orifice fitting and air inlet fitting (Fig. 8) have
not been inadvertently exchanged. The fixed orifice
fitting is light grey in color and is located atrearof
valve cover. The air inlet fitting is black in color and
is located atfrontof valve cover.
(1) Pull fixed orifice fitting (Fig. 8) from valve
cover and leave tube attached.
(2) Start engine and bring to idle speed.
(3) If fitting is not plugged, a hissing noise will be
heard as air passes through fitting orifice. Also, a
strong vacuum should be felt with a finger placed at
fitting inlet.
(4) If vacuum is not present, remove fitting orifice
fitting from tube. Start engine. If vacuum can now be
felt, replace fixed orifice fitting. Do not attempt to
clean plastic fitting.
(5) If vacuum is still not felt at hose, check line/
hose for kinks or for obstruction. If necessary, clean
out intake manifold fitting at intake manifold. Do
this by turning a 1/4 inch drill (by hand) through the
fitting to dislodge any solid particles. Blow out thefitting with shop air. If necessary, use a smaller drill
to avoid removing any metal from the fitting.
(6) Return fixed orifice fitting to valve cover and
leave tube attached.
(7) Disconnect air inlet fitting and its attached
hose at front of valve cover (Fig. 8). Start engine and
bring to idle speed. Hold a piece of stiff paper (such
as a parts tag) loosely over the rubber grommet
(opening) of the disconnected air inlet fitting.
(8) The paper should be drawn against the rubber
grommet with noticeable force. This will be after
allowing approximately one minute for crankcase
pressure to reduce.
(9) If vacuum is not present, check breather hoses/
tubes/lines for obstructions or restrictions.
(10) After testing, reconnect all system hoses/
tubes/lines.
REMOVAL - FIXED ORIFICE FITTING
When installing fixed orifice fitting, be sure loca-
tions of fixed orifice fitting and air inlet fitting (Fig.
9) have not been inadvertently exchanged. The fixed
orifice fitting is light grey in color and is located at
rearof valve cover. The air inlet fitting is black in
color and is located atfrontof valve cover.
(1) Pull fixed orifice fitting (Fig. 9) from valve
cover grommet.
(2) Separate fitting from CCV breather tube.
Fig. 8 Fixed Orifice Fitting and CCV SystemÐ4.0L
Engine
1 - AIR INLET FITTING
2 - FIXED ORIFICE FITTING
3 - CCV BREATHER TUBE (REAR)
4 - INT. MAN. FITTING
5 - CCV BREATHER TUBE (FRONT)
Fig. 9 FIXED ORIFICE FITTING - 4.0L
1 - AIR INLET FITTING
2 - FIXED ORIFICE FITTING
3 - CCV BREATHER TUBE (REAR)
4 - INT. MAN. FITTING
5 - CCV BREATHER TUBE (FRONT)
25 - 28 EVAPORATIVE EMISSIONSWJ

CAUTION: Remove the fuel tank filler tube cap to
relieve fuel tank pressure. The cap must be
removed prior to disconnecting any fuel system
component or before draining the fuel tank.
LEAK DETECTION PUMP
DESCRIPTION
The evaporative emission system is designed to
prevent the escape of fuel vapors from the fuel sys-
tem (Fig. 11). Leaks in the system, even small ones,
can allow fuel vapors to escape into the atmosphere.
Government regulations require onboard testing to
make sure that the evaporative (EVAP) system is
functioning properly. The leak detection system tests
for EVAP system leaks and blockage. It also performs
self-diagnostics. During self-diagnostics, the Power-
train Control Module (PCM) first checks the Leak
Detection Pump (LDP) for electrical and mechanical
faults. If the first checks pass, the PCM then uses
the LDP to seal the vent valve and pump air into the
system to pressurize it. If a leak is present, the PCM
will continue pumping the LDP to replace the air
that leaks out. The PCM determines the size of the
leak based on how fast/long it must pump the LDP
as it tries to maintain pressure in the system.
EVAP LEAK DETECTION SYSTEM COMPONENTS
Service Port: Used with special tools like the Miller
Evaporative Emissions Leak Detector (EELD) to test
for leaks in the system.
EVAP Purge Solenoid: The PCM uses the EVAP
purge solenoid to control purging of excess fuel
vapors stored in the EVAP canister. It remains closed
during leak testing to prevent loss of pressure.
EVAP Canister: The EVAP canister stores fuel
vapors from the fuel tank for purging.
EVAP Purge Orifice: Limits purge volume.
EVAP System Air Filter: Provides air to the LDP
for pressurizing the system. It filters out dirt while
allowing a vent to atmosphere for the EVAP system.
Fig. 11 TYPICAL SYSTEM COMPONENTS
1 - Throttle Body
2 - Service Vacuum Supply Tee (SVST)
3 - LDP Solenoid
4 - EVAP System Air Filter
5 - LDP Vent Valve
6 - EVAP Purge Orifice
7 - EVAP Purge Solenoid
8 - Service Port
9 - To Fuel Tank
10 - EVAP Canister
11 - LDP
12 - Intake Air Plenum
25 - 30 EVAPORATIVE EMISSIONSWJ
FUEL FILLER CAP (Continued)

OPERATION
The main purpose of the LDP is to pressurize the
fuel system for leak checking. It closes the EVAP sys-
tem vent to atmospheric pressure so the system can
be pressurized for leak testing. The diaphragm is
powered by engine vacuum. It pumps air into the
EVAP system to develop a pressure of about 7.59
H2O (1/4) psi. A reed switch in the LDP allows the
PCM to monitor the position of the LDP diaphragm.
The PCM uses the reed switch input to monitor how
fast the LDP is pumping air into the EVAP system.
This allows detection of leaks and blockage. The LDP
assembly consists of several parts (Fig. 12). The sole-
noid is controlled by the PCM, and it connects the
upper pump cavity to either engine vacuum or atmo-
spheric pressure. A vent valve closes the EVAP sys-
tem to atmosphere, sealing the system during leak
testing. The pump section of the LDP consists of a
diaphragm that moves up and down to bring air in
through the air filter and inlet check valve, and
pump it out through an outlet check valve into the
EVAP system. The diaphragm is pulled up by engine
vacuum, and pushed down by spring pressure, as the
LDP solenoid turns on and off. The LDP also has a
magnetic reed switch to signal diaphragm position to
the PCM. When the diaphragm is down, the switch is
closed, which sends a 12 V (system voltage) signal to
the PCM. When the diaphragm is up, the switch is
open, and there is no voltage sent to the PCM. This
allows the PCM to monitor LDP pumping action as it
turns the LDP solenoid on and off.
LDP AT REST (NOT POWERED)
When the LDP is at rest (no electrical/vacuum) the
diaphragm is allowed to drop down if the internal
(EVAP system) pressure is not greater than the
return spring. The LDP solenoid blocks the engine
vacuum port and opens the atmospheric pressure
port connected through the EVAP system air filter.
The vent valve is held open by the diaphragm. This
allows the canister to see atmospheric pressure (Fig.
13).
DIAPHRAGM UPWARD MOVEMENT
When the PCM energizes the LDP solenoid, the
solenoid blocks the atmospheric port leading through
the EVAP air filter and at the same time opens the
engine vacuum port to the pump cavity above the
diaphragm. The diaphragm moves upward when vac-
uum above the diaphragm exceeds spring force. This
upward movement closes the vent valve. It also
causes low pressure below the diaphragm, unseating
the inlet check valve and allowing air in from the
EVAP air filter. When the diaphragm completes its
upward movement, the LDP reed switch turns from
closed to open (Fig. 14).
DIAPHRAGM DOWNWARD MOVEMENT
Based on reed switch input, the PCM de-energizes
the LDP solenoid, causing it to block the vacuum
port, and open the atmospheric port. This connects
the upper pump cavity to atmosphere through the
EVAP air filter. The spring is now able to push the
diaphragm down. The downward movement of the
diaphragm closes the inlet check valve and opens the
outlet check valve pumping air into the evaporative
system. The LDP reed switch turns from open to
closed, allowing the PCM to monitor LDP pumping
(diaphragm up/down) activity (Fig. 15). During the
pumping mode, the diaphragm will not move down
far enough to open the vent valve. The pumping cycle
is repeated as the solenoid is turned on and off.
When the evaporative system begins to pressurize,
the pressure on the bottom of the diaphragm will
begin to oppose the spring pressure, slowing the
pumping action. The PCM watches the time from
when the solenoid is de-energized, until the dia-
phragm drops down far enough for the reed switch to
Fig. 12 EVAP LEAK DETECTION SYSTEM
COMPONENTS
1 - Reed Switch
2 - Solenoid
3 - Spring
4 - Pump Cavity
5 - Diaphragm
6 - Inlet Check Valve
7 - Vent Valve
8 - From Air Filter
9 - To Canister
10 - Outlet Check Valve
11 - Engine Vacuum
WJEVAPORATIVE EMISSIONS 25 - 31
LEAK DETECTION PUMP (Continued)

change from opened to closed. If the reed switch
changes too quickly, a leak may be indicated. The
longer it takes the reed switch to change state, the
tighter the evaporative system is sealed. If the sys-
tem pressurizes too quickly, a restriction somewhere
in the EVAP system may be indicated.
PUMPING ACTION
Action : During portions of this test, the PCM uses
the reed switch to monitor diaphragm movement.
The solenoid is only turned on by the PCM after the
reed switch changes from open to closed, indicating
that the diaphragm has moved down. At other times
during the test, the PCM will rapidly cycle the LDP
solenoid on and off to quickly pressurize the system.
During rapid cycling, the diaphragm will not move
enough to change the reed switch state. In the state
of rapid cycling, the PCM will use a fixed time inter-
val to cycle the solenoid. If the system does not pass
the EVAP Leak Detection Test, the following DTCs
may be set:
²P0442 - EVAP LEAK MONITOR 0.0409LEAK
DETECTED
²P0455 - EVAP LEAK MONITOR LARGE LEAK
DETECTED²P0456 - EVAP LEAK MONITOR 0.0209LEAK
DETECTED
²P1486 - EVAP LEAK MON PINCHED HOSE
FOUND
²P1494 - LEAK DETECTION PUMP SW OR
MECH FAULT
²P1495 - LEAK DETECTION PUMP SOLENOID
CIRCUIT
DIAGNOSIS AND TESTING - ENABLING
CONDITIONS TO RUN EVAP LEAK DETECTION
TEST
²Cold start: with ambient temperature (obtained
from modeling the inlet air temperature sensor on
passenger vehicles and the battery temperature sen-
sor on Jeep & Dodge Truck vehicles) between 4É C
(40É F) and 32É C (90É F) for 0.040 leak. Between 4É
C (40É F) and 29É C (85É F) for 0.020 leak.
²Engine coolant temperature within:-12É to -8É C
(10É to 18É F) of battery/ambient.
²Battery voltage between 10 and 15 volts.
²Low fuel warning light off (fuel level must be
between 15% and 85%.
²MAP sensor reading 22 in Hg or above (This is
the manifold absolute pressure, not vacuum).
Fig. 13 LDP AT REST
1 - Diaphragm
2 - Inlet Check Valve (Closed)
3 - Vent Valve (Open)
4 - From Air Filter
5 - To Canister
6 - Outlet Check Valve (Closed)
7 - Engine Vacuum (Closed)
Fig. 14 DIAPHRAGM UPWARD MOVEMENT
1 - Diaphragm
2 - Inlet Check Valve (Open)
3 - Vent Valve (Closed)
4 - From Air Filter
5 - To Canister
6 - Outlet Check Valve (Closed)
7 - Engine Vacuum (Open)
25 - 32 EVAPORATIVE EMISSIONSWJ
LEAK DETECTION PUMP (Continued)

MIL will illuminate, and the remaining EVAP Leak
Detection Test is canceled.
SECTION 2 - P1494 Leak Detection Pump
Switch or Mechanical Fault-If DTC P1495 is not
set, the PCM will check for DTC P1494. If the LDP
reed switch was closed when the key was turned to
9ON9, the PCM energizes the LDP solenoid for up to
8 seconds and monitors the LDP switch. As the LDP
diaphragm is pulled up by engine vacuum, the LDP
reed switch should change from closed to open. If it
does not, the PCM sets a temporary fault (P1494) in
memory, and waits until the next time the Enabling
Conditions are met to run the test again. If this is
again detected, P1494 is stored and the MIL is illu-
minated. If the problem is not detected during the
next enabling cycle, the temporary fault will be
cleared.
However, if the PCM detects the reed switch open
when the key is turned to9ON9, the PCM must deter-
mine if this condition is due to residual pressure in
the EVAP system, or an actual fault. The PCM stores
information in memory on EVAP system purging
from previous engine run or drive cycles.
If little or no purging took place, residual pressure
could be holding the LDP diaphragm up, causing the
LDP switch to be open. Since this is not a malfunc-
tion, the PCM cancels the EVAP Leak Detection Test
without setting the temporary fault.
If there was sufficient purging during the previous
cycle to eliminate EVAP system pressure, the PCM
judges that this is a malfunction and sets a tempo-
rary fault in memory. The next time that the
Enabling Conditions are met, the test will run again.
If the fault is again detected, the MIL will illuminate
and DTC P1494 will be stored. If the fault is not
detected, the temporary fault will be cleared.
SECTION 3 - P1486 EVAP Leak Monitor
Pinched Hose Found-If no fault has been detected
so far, the PCM begins testing for possible blockage
in the EVAP system between the LDP and the fuel
tank. This is done by monitoring the time required
for the LDP to pump air into the EVAP system dur-
ing two to three pump cycles. If no blockage is
present, the LDP diaphragm is able to quickly pump
air out of the LDP each time the PCM turns off the
LDP solenoid. If a blockage is present, the PCM
detects that the LDP takes longer to complete each
pump cycle. If the pump cycles take longer than
expected (approximately 6 to 10 seconds) the PCM
will suspect a blockage. On the next drive when
Enabling Conditions are met, the test will run again.
If blockage is again detected, P1486 is stored, and
the MIL is illuminated.
SECTION4-NoDTCCanBeSetDuring This
Time-After the LDP blockage tests are completed,
the PCM then tests for EVAP system leakage. First,the PCM commands the LDP to rapidly pump for 20
to 50 seconds (depending on fuel level) to build pres-
sure in the EVAP system. This evaluates the system
J18-24-0 to see if it can be sufficiently pressurized.
This evaluation (rapid pump cycling) may occur sev-
eral times prior to leak checking. The LDP reed
switch does not close and open during rapid pumping
because the diaphragm does not travel through its
full range during this part of the test.
SECTION 5 - P0456, P0442, P0455 EVAP Leak
Monitor and Leak Detected-Next, the PCM per-
forms one or more test cycles by monitoring the time
required for the LDP reed switch to close (diaphragm
to drop) after the LDP solenoid is turned off.
If the switch does not close, or closes after a long
delay, it means that the system does not have any
significant leakage and the EVAP Leak Detection
Test is complete.
However, if the LDP reed switch closes quickly,
there may be a leak or the fuel level may be low
enough that the LDP must pump more to finish pres-
surizing the EVAP system. In this case, the PCM will
rapidly pump the LDP again to build pressure in the
EVAP system, and follow that by monitoring the time
needed for several LDP test cycles. This process of
rapid pumping followed by several LDP test cycles
may repeat several times before the PCM judges that
a leak is present.
When leaks are present, the LDP test cycle time
will be inversely proportional to the size of the leak.
The larger the leak, the shorter the test cycle time.
The smaller the leak, the longer the test cycle time.
DTC's may be set when a leak as small as 0.5 mm
(0.0209) diameter is present.
If the system detects a leak, a temporary fault will
be stored in PCM memory. The time it takes to detect
a .020, .040, or Large leak is based on calibrations
that vary from model to model. The important point
to remember is if a leak is again detected on the next
EVAP Leak Detection Test, the MIL will illuminate
and a DTC will be stored based on the size of leak
detected. If no leak is detected during the next test,
the temporary fault will be cleared.
DIAGNOSTIC TIPS During diagnosis, you can
compare the LDP solenoid activity with the monitor
sequence in Figure 6. If the PCM detects a problem
that could set a DTC, the testing is halted and LDP
solenoid activity will stop. As each section of the test
begins, it indicates that the previous section passed
successfully. By watching to see which tests complete,
you can see if any conditions are present that the
PCM considers abnormal.
For example, if the LDP solenoid is energized for
the test cycles to test for blockage (P1486), it means
that the LDP has already passed its test for P1494.
Then, if the PCM detects a possible blockage, it will
25 - 34 EVAPORATIVE EMISSIONSWJ
LEAK DETECTION PUMP (Continued)

set a temporary fault without turning on the MIL
and continue the leak portion of the test. However,
the PCM will assume that the system is already
pressurized and skip the rapid pump cycles.
Always diagnose leaks, if possible, before discon-
necting connections. Disconnecting connections may
mask a leak condition.
Keep in mind that if the purge solenoid seat is
leaking, it could go undetected since the leak would
end up in the intake manifold. Disconnect the purge
solenoid at the manifold when leak checking. In addi-
tion, a pinched hose fault (P1486) could set if the
purge solenoid does not purge the fuel system prop-
erly (blocked seat). The purge solenoid must vent the
fuel system prior to the LDP system test. If the
purge solenoid cannot properly vent the system the
LDP cannot properly complete the test for P1486 and
this fault can set due to pressure being in the EVAP
system during the test sequence.
Multiple actuation's of the DRB IIItLeak Detec-
tion Pump (LDP) Monitor Test can hide a 0.020 leak
because of excess vapor generation. Additionally, any
source for additional vapor generation can hide a
small leak in the EVAP system. Excess vapor gener-
ation can delay the fall of the LDP diaphragm thus
hiding the small leak. An example of this condition
could be bringing a cold vehicle into a warm shop for
testing or high ambient temperatures.
Fully plugged and partially plugged underhood
vacuum lines have been known to set MIL condi-
tions. P1494 and P0456 can be set for this reason.
Always, thoroughly, check plumbing for pinches or
blockage before condemning components.
TEST EQUIPMENT The Evaporative Emission
Leak Detector (EELD) Miller Special Tool 8404 is
capable of visually detecting leaks in the evaporative
system and will take the place of the ultrasonic leak
detector 6917A. The EELD utilizes shop air and a
smoke generator to visually detect leaks down to
0.020 or smaller. The food grade oil used to make the
smoke includes an UV trace dye that will leave tell-
tale signs of the leak under a black light. This is
helpful when components have to be removed to
determine the exact leak location. For detailed test
instructions, follow the operators manual packaged
with the EELD.
NOTE: Be sure that the PCM has the latest software
update. Reprogram as indicated by any applicable
Technical Service Bulletin. After LDP repairs are
completed, verify the repair by running the DRB IIIT
Leak Detection Pump (LDP) Monitor Test as
described in Technical Service Bulletin 18-12-99.REMOVAL
The Leak Detection Pump (LDP) is located under
the left quarter panel behind the left/rear wheel (Fig.
16). It is attached to a two-piece support bracket
(Fig. 17). The LDP and LDP filter are replaced (ser-
viced) as one unit.
(1) Remove stone shield behind left/rear wheel
(Fig. 18). Drill out plastic rivets for removal.
(2) Remove 3 LDP mounting bolts (Fig. 19).
(3) Remove support bracket brace bolt (Fig. 17).
(4) Loosen, but do not remove 2 support bracket
nuts at frame rail (Fig. 19).
(5) To separate and lower front section of two-piece
support bracket, remove 3 attaching bolts on bottom
of support bracket (Fig. 17). While lowering support
bracket, disconnect LDP wiring clip (Fig. 20).
(6) Disconnect electrical connector at LDP (Fig.
20).
(7) Carefully remove vapor/vacuum lines at LDP
(Fig. 20).
(8) Remove LDP.
INSTALLATION
The LDP is located in the left quarter panel behind
the left/rear wheel. It is attached to a two-piece sup-
port bracket (Fig. 17). The LDP and LDP filter are
replaced (serviced) as one unit.
(1) Position LDP and carefully install vapor/vac-
uum lines to LDP and LDP filter.The vapor/vac-
uum lines and hoses must be firmly connected.
Fig. 16 LOCATION, LDP / EVAP CANISTER
1 - LEAK DETECTION PUMP
2 - EVAP CANISTER
WJEVAPORATIVE EMISSIONS 25 - 35
LEAK DETECTION PUMP (Continued)