Positive Crankcase Ventilation (Pcv) Systems; Description And Operation; Positive Crankcase Ventilation Valve - Chrysler 2000 LHS Owner's Manual

LH
DESCRIPTION AND OPERATION (Continued)
phragm is in the "down" position the reed switch will
be in its "closed" state. 12 volts is sent to the PCM
via the switch sense circuit.
The check valves are one-way valves. The first
check valve is used to draw outside air into the lower
chamber of the LDP (the space that is below the
pump diaphragm). The second check valve is used to
vent this outside air, which has become pressurized
from the fall of the pump diaphragm, into the evap-
orative system.
The spring loaded vent seal valve, inside the LDP
is used to seal off the evaporative system. When the
pump diaphragm is in the "up" position the spring
pushes the vent seal valve closed. The vent seal valve
opens only when the pump diaphragm is in its "full
down" position. When the pump assembly is in its
pump mode the pump diaphragm is not allowed to
descend (fall) so far as to allow the vent seal valve to
open. This allows the leak detection pump to develop
the required pressure within the evaporative system
for system leak testing.
A pressure build up within the evaporative system
may cause pressure on the lower side of the LDP dia-
phragm. This will cause the LDP diaphragm to
remain in its "up" position (stuck in the up position).
This condition can occur even when the solenoid
valve is deenergized. This condition can be caused by
previous cycling (pumping) of the LDP by the techni-
cian (dealer test). Another way that this condition is
created is immediately following the running of the
vehicle evaporative system monitor. In this case, the
PCM has not yet opened the proportional purge sole-
noid in order to vent the pressure that has been built
up in the evaporative system to the engine combus-
tion system. The technician will need to vent the
evaporative system pressure via the vehicle fuel filler
cap and its fuel filler secondary seal (if so equipped
in the fuel filler neck). This will allow the technician
to cycle the LDP and to watch switch state changes.
After passing the leak detection phase of the test,
system pressure is maintained until the purge sys-
tem is activated, in effect creating a leak. If the dia-
phragm falls (as is expected), causing the reed switch
to change state, then the diagnostic test is completed.
When of the evaporative system leak monitor
begins its various tests, a test is performed to deter-
mine that no part of the evaporative system is
blocked. In this test, the LDP is cycled (pumped) a
calibrated (few) number of times. Pressure should not
build up in the evaporative system. If pressure is
present, then LDP diaphragm is forced to stay in its
"up" position. The reed switch now stays open and
the PCM senses this open (incorrect) state. The evap-
orative system monitor will fail the test because of a
detected obstruction within the system.
EMISSION CONTROL SYSTEMS
Possible causes:
• Open or shorted LDP switch sense circuit
• Leak Detection Pump switch failure
• Open fused ignition switch output
• Restricted, disconnected, or blocked manifold
vacuum source
• Obstruction of hoses or lines
• PCM failure
POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEMS
OPERATION
Intake manifold vacuum removes crankcase vapors
and piston blow-by from the engine. Emissions pass
through the PCV valve into the intake manifold ple-
num (Fig. 4) or (Fig. 5). The vapors become part of
the calibrated air-fuel mixture, are burned and
expelled with the exhaust gases. The air cleaner sup-
plies make up air when the engine does not have
enough vapor or blow-by gases.
It has a heat exchange system to help improve cold
weather operation.
Fig. 4 PCV Valve—2.7L Engine
1 – PCV VALVE

POSITIVE CRANKCASE VENTILATION VALVE

OPERATION
The PCV valve contains a spring loaded plunger.
The plunger meters the amount of crankcase vapors
routed into the combustion chamber based on intake
manifold vacuum.
25 - 23
2000 LHS, 300M, CONCORDE and INTREPID
Publication No. 81-270-0040
TSB 26-10-99 October, 1999