Chrysler Voyager. Manual — part 3

FIGURE 2

9

GENERAL INFORMATION

LEAK DETECTION PUMP SYSTEM — IF
EQUIPPED

The evaporative emission system is designed to

prevent the escape of fuel vapors from the fuel
system. 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 Powertrain 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
(FIGURE 1)

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 pres-
sure.

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.

Leak Detection Pump (LDP) Components:

The main purpose of the LDP is to pressurize the

fuel system for leak checking. It closes the EVAP
system 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 7.5

9

H

2

O (

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-

ure 2). The solenoid is controlled by the PCM, and it
connects the upper pump cavity to either engine
vacuum or atmospheric pressure. A vent valve
closes the EVAP system 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 volt-
age) 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

FIGURE 1

FIGURE 2

10

GENERAL INFORMATION

pressure port connected through the EVAP system
air filter. The vent valve is held open by the dia-
phragm. This allows the canister to see atmospheric
pressure (Figure 3).

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 up-
ward when the vacuum above the diaphragm ex-
ceeds 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 (Figure
4).

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 move-
ment 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-
ure 5). 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 diaphragm drops down far
enough for the reed switch to change from open 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 system pressurizes too
quickly, a restriction somewhere in the EVAP sys-
tem may be indicated.

PUMPING 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

FIGURE 3

FIGURE 4

FIGURE 5

11

GENERAL INFORMATION

of rapid cycling, the PCM will use a fixed time
interval to cycle the solenoid.

If the system does not pass the EVAP Leak

Detection Test, the following DTCs may be set:

•

P0442 - EVAP LEAK MONITOR 0.040

9 LEAK

DETECTED

•

P0455 - EVAP LEAK MONITOR LARGE LEAK
DETECTED

•

P0456 - EVAP LEAK MONITOR 0.020

9 LEAK

DETECTED

•

P1486 - EVAP LEAK MON PINCHED HOSE
FOUND

•

P1494 - LEAK DETECTION PUMP SW OR
MECH FAULT

•

P1495 - LEAK DETECTION PUMP SOLENOID
CIRCUIT

ENABLING CONDITIONS TO RUN EVAP LEAK
DETECTION TEST

1. Cold start: with ambient temperature (obtained

from modeling the inlet air temperature sensor
on passenger vehicles and the battery tempera-
ture sensor on Jeep & truck vehicles) between
4°C (40°F) and 32°C (90°F) for 0.040 leak. Be-
tween 4°C (40°F) and 29°C (85°F) for 0.020 leak.

2. Engine coolant temperature within: -12° to -8°C

(10° to 18°F) of battery/ambient.

3. Battery voltage between 10 and 15 volts.

NOTE: If battery voltage drops below 10 volts
for more than 5 seconds during engine
cranking, the EVAP Leak Detection Test will
not run.

4. Low fuel warning light off (fuel level must be

between 15% and 85%).

5. MAP sensor reading 22 in Hg or above (This is

the manifold absolute pressure, not vacuum).

6. No engine stall during test.

NOTE: The following values are approximate
and vehicle specific. Use the values seen in
pre test/monitor test screen on the DRBIII

T

.

See TSB 25-02-98 for more detail.

A DTC will not set if a one-trip fault is set or if the

MIL is illuminated for any of the following:

•

Purge Solenoid

•

All engine Controller Self Test Faults

•

All Cam and/or Crank Sensor Faults

•

MAP Sensor Faults

•

Ambient/Battery Temperature Sensor Electrical
Faults

•

All Coolant Sensor Faults

•

All TPS Faults

•

LDP Pressure Switch Faults

•

EGR Solenoid Electrical Faults

•

All Injector Faults

•

Baro Out Of Range

•

Vehicle Speed Faults

•

LDP Solenoid Circuit

FIGURE 6 SECTION 1

When the ignition key is turned to “ON”, the LDP

diaphragm should be in the down position and the
LDP reed switch should be closed. If the EVAP
system has residual pressure, the LDP diaphragm
may be up. This could result in the LDP reed switch
being open when the key is turned to “ON” and a
P1494 fault could be set because the PCM is expect-
ing the reed switch to be closed.

After the key is turned “ON”, the PCM immedi-

ately tests the LDP solenoid circuit for electrical
faults. If a fault is detected, DTC P1495 will set, the
MIL will illuminate, and the remaining EVAP Leak
Detection Test is canceled.

NOTE: If battery temperature is not within
range, or if the engine coolant temperature is
not within a specified range of the battery
temperature, the PCM will not run tests for
DTC P1494, P1486, P0442, P0455 and P0441.
These

temperature

calibrations

may

be

different between models.

FIGURE 6 SECTION 2

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 “ON”, the PCM ener-
gizes 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

FIGURE 6

12

GENERAL INFORMATION