Chrysler 300M 2002 Service Manual page 1684

LH
EMISSIONS CONTROL (Continued)
• Fuel level above 15%
• Ambient air temperature
• Barometric pressure
• Engine RPM within acceptable range of desired
idle
Pending Conditions—The Task Manager typi-
cally does not run the Oxygen Sensor Monitor if over-
lapping monitors are running or the MIL is
illuminated for any of the following:
• Misfire Monitor
• Front Oxygen Sensor and Heater Monitor
• MAP Sensor
• Vehicle Speed Sensor
• Engine Coolant Temperature Sensor
• Throttle Position Sensor
• Engine Controller Self Test Faults
• Cam or Crank Sensor
• Injector and Coil
• Idle Air Control Motor
• EVAP Electrical
• EGR Solenoid Electrical (if equipped)
• Intake/inlet Air Temperature
• 5 Volt Feed
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
• Ethanel content learn is takeng place and the
ethenal used once flag is set (if equipped)
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
EMISSIONS CONTROL 25 - 3
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. Voltage to the O2 sensor
begins to increase the temperature. As the sensor
temperature increases,
decreases. The PCM continues biasing the 5 volt sig-
nal to the sensor. 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 with catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
the internal resistance