Dodge ZB 2005, Руководство по обслуживанию

Страница: 1092 / 1873

Conflict—The Task Manager does not run the
Oxygen Sensor Monitor if any of the following condi-
tions are present:
•
A/C ON (A/C clutch cycling temporarily sus-
pends monitor)
•
Purge flow in progress
Suspend—The Task Manager suspends maturing
a fault for the Oxygen Sensor Monitor if any of the
following are present:
•
Oxygen Sensor Heater Monitor, Priority 1
•
Misfire Monitor, Priority 2
OXYGEN SENSOR HEATER MONITOR
DESCRIPTION—If there is an oxygen sensor
(O2S) DTC as well as a O2S heater DTC, the O2S
fault MUST be repaired first. After the O2S fault is
repaired, verify that the heater circuit is operating
correctly.
The voltage readings taken from the O2S are very
temperature sensitive. The readings are not accurate
below 300°C. Heating of the O2S is done to allow the
engine controller to shift to closed loop control as
soon as possible. The heating element used to heat
the O2S must be tested to ensure that it is heating
the sensor properly.
The heater element itself is not tested. The sensor
output is used to test the heater by isolating the
effect of the heater element on the O2S output volt-
age from the other effects. The resistance is normally
between 100 ohms and 4.5 megaohms. When oxygen
sensor temperature increases, the resistance in the
internal circuit decreases. The PCM sends a 5 volts
biased signal through the oxygen sensors to ground
this monitoring circuit. As the temperature increases,
resistance decreases and the PCM detects a lower
voltage at the reference signal. Inversely, as the tem-
perature decreases, the resistance increases and the
PCM detects a higher voltage at the reference signal.
The O2S circuit is monitored for a drop in voltage.
OPERATION—The Oxygen Sensor Heater Moni-
tor begins after the ignition has been turned OFF.
The PCM sends a 5 volt bias to the oxygen sensor
every 1.6 seconds. The PCM keeps it biased for 35
ms each time. As the sensor cools down, the resis-
tance increases and the PCM reads the increase in
voltage. Once voltage has increased to a predeter-
mined amount, higher than when the test started,
the oxygen sensor is cool enough to test heater oper-
ation.
When the oxygen sensor is cool enough, the PCM
energizes the ASD relay and uses a pulse-width mod-
ulated signal to control the ground side of the O2
sensor. Voltage to the O2 sensor begins to increase
the
temperature. As the sensor temperature
increases, the internal resistance decreases. The
PCM continues biasing the 5 volt signal to the sen-
sor. Each time the signal is biased, the PCM reads a
voltage decrease. When the PCM detects a voltage
decrease of a predetermined value for several biased
pulses, the test passes.
The heater elements are tested each time the
engine is turned OFF if all the enabling conditions
are met. If the monitor fails, the PCM stores a
maturing fault and a Freeze Frame is entered. If two
consecutive tests fail, a DTC is stored. Because the
ignition is OFF, the MIL is illuminated at the begin-
ning of the next key cycle.
Enabling Conditions—The following conditions
must be met for the PCM to run the oxygen sensor
heater test:
•
Engine run time of at least 3 minutes
•
Engine run time at a predetermind speed and
throttle opening.
•
Key OFF power down
•
Battery voltage of at least 10 volts
•
Sufficient Oxygen Sensor cool down
Pending Conditions—There are not conditions or
situations that prompt conflict or suspension of test-
ing. The oxygen sensor heater test is not run pending
resolution of MIL illumination due to oxygen sensor
failure.
Suspend—There are no conditions which exist for
suspending the Heater Monitor.
CATALYST MONITOR
To comply with clean air regulations, vehicles are
equipped three way catalytic converter (TWC).These
converters reduce the emission of hydrocarbons,
oxides of nitrogen 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
ZB
EMISSIONS CONTROL 25 - 3
EMISSIONS CONTROL (Continued)