fuel cap DODGE NEON 2000 Service Owner's Manual

Pending ConditionsÐThere are not conditions
or situations that prompt conflict or suspension of
testing. The oxygen sensor heater test is not run
pending resolution of MIL illumination due to oxygen
sensor failure.
SuspendÐThere are no conditions which exist for
suspending the Heater Monitor.
CATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
Normal vehicle miles or engine misfire can cause a
catalyst to decay. A meltdown of the ceramic core can
cause a reduction of the exhaust passage. This can
increase vehicle emissions and deteriorate engine
performance, driveability and fuel economy.
The catalyst monitor uses dual oxygen sensors
(O2S's) to monitor the efficiency of the converter. The
dual O2S strategy is based on the fact that as a cat-
alyst deteriorates, its oxygen storage capacity and its
efficiency are both reduced. By monitoring the oxy-
gen storage capacity of a catalyst, its efficiency can
be indirectly calculated. The upstream O2S is used to
detect the amount of oxygen in the exhaust gas
before the gas enters the catalytic converter. The
PCM calculates the A/F mixture from the output of
the O2S. A low voltage indicates high oxygen content
(lean mixture). A high voltage indicates a low content
of oxygen (rich mixture).
When the upstream O2S detects a lean condition,
there is an abundance of oxygen in the exhaust gas.
A functioning converter would store this oxygen so it
can use it for the oxidation of HC and CO. As the
converter absorbs the oxygen, there will be a lack of
oxygen downstream of the converter. The output of
the downstream O2S will indicate limited activity in
this condition.
As the converter loses the ability to store oxygen,
the condition can be detected from the behavior of
the downstream O2S. When the efficiency drops, no
chemical reaction takes place. This means the con-
centration of oxygen will be the same downstream as
upstream. The output voltage of the downstream
O2S copies the voltage of the upstream sensor. The
only difference is a time lag (seen by the PCM)
between the switching of the O2S's.
To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S's is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For atotally ineffective catalyst, this ratio will be one-to-
one, indicating that no oxidation occurs in the device.
The system must be monitored so that when cata-
lyst efficiency deteriorates and exhaust emissions
increase to over the legal limit, the MIL (check
engine lamp) will be illuminated.
Monitor OperationÐTo monitor catalyst effi-
ciency, the PCM expands the rich and lean switch
points of the heated oxygen sensor. With extended
switch points, the air/fuel mixture runs richer and
leaner to overburden the catalytic converter. Once
the test is started, the air/fuel mixture runs rich and
lean and the O2 switches are counted. A switch is
counted when an oxygen sensor signal goes from
below the lean threshold to above the rich threshold.
The number of Rear O2 sensor switches is divided by
the number of Front O2 sensor switches to determine
the switching ratio.
The test runs for 20 seconds. As catalyst efficiency
deteriorated over the life of the vehicle, the switch
rate at the downstream sensor approaches that of the
upstream sensor. If at any point during the test
period the switch ratio reaches a predetermined
value, a counter is incremented by one. The monitor
is enabled to run another test during that trip. When
the test fails three times, the counter increments to
three, a malfunction is entered, and a Freeze Frame
is stored. When the counter increments to three dur-
ing the next trip, the code is matured and the MIL is
illuminated. If the test passes the first, no further
testing is conducted during that trip.
The MIL is extinguished after three consecutive
good trips. The good trip criteria for the catalyst
monitor is more stringent than the failure criteria. In
order to pass the test and increment one good trip,
the downstream sensor switch rate must be less than
80% of the upstream rate (60% for manual transmis-
sions). The failure percentages are 90% and 70%
respectively.
Enabling ConditionsÐThe following conditions
must typically be met before the PCM runs the cat-
alyst monitor. Specific times for each parameter may
be different from engine to engine.
²Accumulated drive time
²Enable time
²Ambient air temperature
²Barometric pressure
²Catalyst warm-up counter
²Engine coolant temperature
²Accumulated throttle position sensor
²Vehicle speed
²MAP
²RPM
²Engine in closed loop
²Fuel level
25 - 22 EMISSION CONTROL SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)

The proportional purge solenoid operates at a fre-
quency of 200 hz and is controlled by an engine con-
troller circuit that senses the current being applied
to the proportional purge solenoid (Fig. 2) and then
adjusts that current to achieve the desired purge
flow. The proportional purge solenoid controls the
purge rate of fuel vapors from the vapor canister and
fuel tank to the engine intake manifold.
LEAK DETECTION PUMP
DESCRIPTION
The leak detection pump is a device used to detect
a leak in the evaporative system.
The pump contains a 3 port solenoid, a pump that
contains a switch, a spring loaded canister vent valve
seal, 2 check valves and a spring/diaphragm.
OPERATION
Immediately after a cold start, when the engine
temperature is between 40ÉF and 86ÉF, the 3 port
solenoid is briefly energized. This initializes the pump
by drawing air into the pump cavity and also closes
the vent seal. During non-test test conditions, the
vent seal is held open by the pump diaphragm assem-
bly which pushes it open at the full travel position.
The vent seal will remain closed while the pump is
cycling. This is due to the operation of the 3 port sole-
noid which prevents the diaphragm assembly from
reaching full travel. After the brief initialization
period, the solenoid is de-energized, allowing atmo-
spheric pressure to enter the pump cavity. This per-
mits the spring to drive the diaphragm which forces
air out of the pump cavity and into the vent system.
When the solenoid is energized and de-energized, the
cycle is repeated creating flow in typical diaphragm
pump fashion. The pump is controlled in 2 modes:
1 ± FUEL CAP
2 ± RECIRCULATION TUBE
3 ± LIQUID SEPARATOR
4 ± PURGE
5 ± W/LDP
6 ± BREATHER ELEMENT
7 ± W/O LDP8 ± CANISTER
9 ± ROLLOVER VALVE
10 ± FUEL TANK
11 ± CHECK VALVE
12 ± LIQUID TRAP
13 ± CONTROL VALVE
ORVR System Schematic
25 - 26 EMISSION CONTROL SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)

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 ªupº position the spring
pushes the vent seal valve closed. The vent seal valve
opens only when the pump diaphragm is in its ªfull
downº 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 ªupº 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
ªupº 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.
Possible causes:
²Open or shorted LDP switch sense circuit
²Leak Detection Pump switch failure²Open fused ignition switch output
²Restricted, disconnected, or blocked manifold
vacuum source
²Obstruction of hoses or lines
²PCM failure
POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEMS
DESCRIPTION
OPERATION
Intake manifold vacuum removes crankcase vapors
and piston blow-by from the engine. The emissions
pass through the PCV valve into the intake manifold
where they become part of the calibrated air-fuel
mixture. They are burned and expelled with the
exhaust gases. The air cleaner supplies make up air
when the engine does not have enough vapor or
blow-by gases. In this system, fresh air does not
enter the crankcase.
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.
When the engine is not operating or during an
engine backfire, the spring forces the plunger back
against the seat. This prevents vapors from flowing
through the valve (Fig. 4).
When the engine is at idle or cruising, high mani-
fold vacuum is present. At these times manifold vac-
uum is able to completely compress the spring and
Fig. 3 PCV System
25 - 28 EMISSION CONTROL SYSTEMSPL
DESCRIPTION AND OPERATION (Continued)