Chrysler 2005 Crossfire SRT6 Service Manual page 4299

25 - 6 EMISSIONS CONTROL
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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 voltage 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 air/fuel mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunc-
tioning sensor could have difficulty changing beyond the threshold value. Many times, the condition is only tempo-
rary and the sensor will recover. Under normal conditions the voltage signal surpasses the threshold and a counter
is incremented by one. This is called the Half Cycle Counter.
OPERATION - As the Oxygen Sensor signal 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 a
Freeze Frame is stored. Only one counter reaching its predetermined value is needed for the monitor to pass.
The Oxygen Sensor Signal Monitor is a 2 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.
OXYGEN SENSOR HEATER MONITOR
DESCRIPTION - If the Oxygen Sensor (O2S) DTC as well as a O2S heater DTC is present, the O2S Heater DTC
MUST be repaired first. After the O2S Heater is repaired, verify that the sensor circuit is operating correctly.
Note: The O2S Heaters are kept off at coolant temperatures below 20°C (68°F) and at high engine rpm in
order to avoid damaging the heaters. The voltage reading taken from the O2S are very temperature sensitive.
The readings taken from the O2S are not accurate below 300°C (572°F). Heating 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 resistance is checked by the PCM almost
immediately after the engine is started. The same O2S heater return pin used to read the heater resistance is capa-
ble of detecting an open, shorted high or shorted low circuit.
OPERATION - The Oxygen Sensor Heater Monitor begins after the ignition has been turned OFF and the O2 sen-
sors have cooled. As the sensor cools down, the resistance increases and the PCM reads the increase in voltage.
Once voltage has increased to a predetermined amount, higher than when the test started, the oxygen sensor is
cool enough to test heater operation.
When the oxygen sensor is cool enough, the PCM provides a ground path for the O2S heater circuit. Voltage to the
O2 sensor begins to increase the temperature. As the sensor temperature increases, the internal resistance
decreases.
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 beginning of the next key cycle, after the 2nd
failure.
EGR MONITOR
The Powertrain Control Module (PCM) performs an on-board diagnostic check of the EGR system.
The EGR monitor is used to test whether the EGR system is operating within specifications. The diagnostic check
activates only during selected engine/driving conditions. When the conditions are met, the EGR is turned off (sole-
noid de-energized) and the O2S compensation control is monitored. Turning off the EGR shifts the air/fuel ratio in
the lean direction. The O2S data should indicate an increase in the O2 concentration in the combustion chamber
when the exhaust gases are no longer recirculated. While this test does not directly measure the operation of the
EGR system, it can be inferred from the shift in the O2S data whether the EGR system is operating correctly.
Because the O2S is being used, the O2S test must pass its test before the EGR test. This monitor also looks at
EGR linear potentiometer for feedback.
MISFIRE MONITOR
Excessive engine misfire results in increased catalyst temperature and causes an increase in HC emissions. Severe
misfires could cause catalyst damage. To prevent catalytic convertor damage, the PCM monitors engine misfire.