Chrysler 2005 Crossfire SRT6 Service Manual page 2993

ZH FUEL INJECTION 14 - 55
The O2 Sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas. When
a large amount of oxygen is present (caused by a lean air/fuel mixture, can be caused by misfire and exhaust
leaks), the sensors produces a low voltage. When there is a lesser amount of oxygen present (caused by a rich
air/fuel mixture, can be caused by internal engine problems) it produces a higher voltage. By monitoring the oxygen
content and converting it to electrical voltage, the sensors act as a rich-lean switch.
The O2 Sensors are equipped with a heating element that keeps the sensors at proper operating temperature dur-
ing all operating modes. Maintaining correct sensor temperature at all times allows the system to enter into closed
loop operation sooner. Also, it allows the system to remain in closed loop operation during periods of extended idle.
In Closed Loop operation the PCM monitors the O2 Sensors input (along with other inputs) and adjusts the injector
pulse width accordingly. During Open Loop operation the PCM ignores the O2 Sensor input. The PCM adjusts injec-
tor pulse width based on preprogrammed (fixed) values and inputs from other sensors.
The Engine Control Relay located in the Relay Control Module supplies battery voltage to both the upstream and
downstream heated O2 Sensors. The O2 Sensors are equipped with a heating element. The heating elements
reduce the time required for the sensors to reach operating temperature. The PCM uses pulse width modulation to
control the ground side of the heater to regulate the temperature.
UPSTREAM OXYGEN SENSOR
The input from the upstream heated O2 Sensor tells the PCM the oxygen content of the exhaust gas. Based on this
input, the PCM fine tunes the air-fuel ratio by adjusting injector pulse width.
The sensor output varies from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust
manifold. When a large amount of oxygen is present (caused by a lean air-fuel mixture), the sensor produces volt-
age as low as 0.1 volt. When there is a lesser amount of oxygen present (rich air-fuel mixture) the sensor produces
a voltage as high as 1.0 volt. By monitoring the oxygen content in the exhaust gases and comparing that to the
oxygen content in ambient air and converting it to electrical voltage, the sensor acts as a rich-lean switch.
The heating element in the sensor provides heat to the sensor ceramic element. Heating the sensor allows the
system to enter into closed loop operation sooner. Also, it allows the system to remain in closed loop operation
during periods of extended idle.
In Closed Loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with
other signals. In Open Loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and
inputs from other sensors.
DOWNSTREAM OXYGEN SENSOR
The downstream heated O2 Sensor signal is used to detect catalytic convertor deterioration. As the convertor dete-
riorates, the signal from the downstream sensor begins to match the upstream sensor signal except for a slight time
delay. By comparing the downstream heated oxygen sensor signal to the signal from the upstream sensor, the PCM
calculates catalytic convertor efficiency. This calculation is also used to establish the upstream O2 goal voltage
(switching point).