Chrysler 300M 2002 Service Manual page 1683

25 - 2 EMISSIONS CONTROL
EMISSIONS CONTROL (Continued)
• Intake/inlet Air Temperature (IAT) Sensor
• Throttle Position (TPS) Sensor
• Ambient/Battery Temperature Sensors
• Power Steering Switch
• Oxygen Sensor Heater
• Engine Controller
• Brake Switch
• Leak Detection Pump Switch (if equipped)
• P/N Switch
• Trans Controls
Output Functionality—PCM outputs are tested
for functionality in addition to testing for opens and
shorts. When the PCM provides a voltage to an out-
put component, it can verify that the command was
carried out by monitoring specific input signals for
expected changes. For example, when the PCM com-
mands the Idle Air Control (IAC) Motor to a specific
position under certain operating conditions, it expects
to see a specific (target) idle speed (RPM). If it does
not, it stores a DTC.
PCM outputs monitored for functionality include:
• Fuel Injectors
• Ignition Coils
• Torque Converter Clutch Solenoid
• Idle Air Control
• Purge Solenoid
• EGR Solenoid (if equipped)
• LDP Solenoid (if equipped)
• Radiator Fan Control
• Trans Controls
OXYGEN SENSOR (O2S) MONITOR
DESCRIPTION—Effective
emissions is achieved by an oxygen feedback system.
The most important element of the feedback system
is the O2S. The O2S is located in the exhaust path.
Once it reaches operating temperature 300° to 350°C
(572° to 662°F), the sensor generates a voltage that
is inversely proportional to the amount of oxygen in
the exhaust. When there is a large amount of oxygen
in the exhaust caused by a lean condition, the sensor
produces a low voltage, below 450 mV. When the oxy-
gen content is lower, caused by a rich condition, the
sensor produces a higher voltage, above 450mV.
The information obtained by the sensor is used to
calculate the fuel injector pulse width. The PCM is
programmed to maintain the optimum air/fuel ratio.
At this mixture ratio, the catalyst works best to
remove hydrocarbons (HC), carbon monoxide (CO)
and nitrous oxide (NOx) from the exhaust.
The O2S is also the main sensing element for the
EGR (if equipped), Catalyst and Fuel Monitors.
The O2S may fail in any or all of the following
manners:
• Slow response rate (Big Slope)
• Reduced output voltage (Half Cycle)
control of exhaust
• Heater Performance
Slow Response Rate (Big Slope)—Response rate
is the time required for the sensor to switch from
lean to rich signal output once it is exposed to a
richer than optimum A/F mixture or vice versa. As
the PCM adjusts the air/fuel ratio, the sensor must
be able to rapidly detect the change. As the sensor
ages, it could take longer to detect the changes in the
oxygen content of the exhaust gas. The rate of
change that an oxygen sensor experiences is called
"Big Slope". The PCM checks the oxygen sensor volt-
age in increments of a few milliseconds.
Reduced Output Voltage (Half Cycle)—The
output voltage of the O2S ranges from 0 to 1 volt. A
good sensor can easily generate any output voltage in
this range as it is exposed to different concentrations
of oxygen. To detect a shift in the A/F mixture (lean
or rich), the output voltage has to change beyond a
threshold value. A malfunctioning sensor could have
difficulty changing beyond the threshold value. Each
time the voltage signal surpasses the threshold, a
counter is incremented by one. This is called the Half
Cycle Counter.
Heater Performance—The heater is tested by a
separate monitor. Refer to the Oxygen Sensor Heater
Monitor.
OPERATION—As
switches, the PCM monitors the half cycle and big
slope signals from the oxygen sensor. If during the
test neither counter reaches a predetermined value, a
malfunction is entered and Freeze Frame data is
stored. Only one counter reaching its predetermined
value is needed for the monitor to pass.
The Oxygen Sensor Monitor is a two trip monitor
that is tested only once per trip. When the Oxygen
Sensor fails the test in two consecutive trips, the
MIL is illuminated and a DTC is set. The MIL is
extinguished when the Oxygen Sensor monitor
passes in three consecutive trips. The DTC is erased
from memory after 40 consecutive warm-up cycles
without test failure.
Enabling Conditions—The following conditions
must typically be met for the PCM to run the oxygen
sensor monitor:
• Battery voltage
• Engine temperature
• Engine run time
• Engine run time at a predetermined speed
• Engine run time at a predetermined speed and
throttle opening
• Transmission in gear and brake depressed (auto-
matic only)
• Fuel system in Closed Loop
• Long Term Adaptive (within parameters)
• Power Steering Switch in low PSI (no load)
• Engine at idle
the Oxygen Sensor
LH
signal