Operation - Chrysler 300M Service Manual

14 - 30 FUEL INJECTION
O2 SENSOR (Continued)
Fig. 19 Upstream Heated Oxygen Sensor 1/1
1 - PROPORTIONAL PURGE SOLENOID
2 - O2 SENSOR
The downstream heated oxygen sensor threads into
the outlet pipe at the rear of the catalytic convertor
(Fig. 20).
Fig. 20 Downstream Heated Oxygen Sensors—1/2
(R) 2/2 (L)
1 - OXYGEN SENSORS

OPERATION

For SBEC vehicles a single sensor ground is used
for all 4 O2 sensors (6 Cyl.). A seperate upstream and
downstream grounds are used on the NGC vehicles
(4 Cyl.).
As vehicles accumulate mileage, the catalytic con-
vertor deteriorates. The deterioration results in a
less efficient catalyst. To monitor catalytic convertor
deterioration, the fuel injection system uses two
heated oxygen sensors. One sensor upstream of the
catalytic convertor, one downstream of the convertor.
The PCM compares the reading from the sensors to
calculate the catalytic convertor oxygen storage
capacity and converter efficiency. Also, the PCM uses
the upstream heated oxygen sensor input when
adjusting injector pulse width.
When the catalytic converter efficiency drops below
emission standards, the PCM stores a diagnostic
trouble code and illuminates the malfunction indica-
tor lamp (MIL).
The O2 sensors produce voltages from 0 to 1 volt
(this voltage is offset by a constant 2.5 volts on NGC
vehicles), 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 oxy-
gen content and converting it to electrical voltage,
the sensors act as a rich-lean switch.
The oxygen sensors are equipped with a heating
element that keeps the sensors at proper operating
temperature during 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 injector pulse width based on pre-
programmed (fixed) values and inputs from other
sensors.
1.6L Siemens controller and SBEC controller - The
Automatic Shutdown (ASD) relay supplies battery
voltage to both the upstream and downstream heated
oxygen sensors. The oxygen 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 on 4 cyl. upstream O2 heater only.
NGC Controller - Has a common ground for the
heater in the O2S. 12 volts is supplied to the heater
in the O2S by the NGC controller. Both the upstream
and downstream O2 sensors for NGC are pulse width
modulation (PWM).
LH