Chrysler neon 1997 Service Manual page 559

14 - 30 FUEL SYSTEM
DESCRIPTION AND OPERATION (Continued)
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 inputs. In Open Loop, the
PCM adjusts injector pulse width based on prepro-
grammed (fixed) values and inputs from other sen-
sors.
The upstream oxygen sensor threads into the out-
let flange of the exhaust manifold (Fig. 11).
Fig. 11 Upstream Heated Oxygen Sensor
DOWNSTREAM OXYGEN SENSOR
The downstream heated oxygen sensor threads into
the outlet pipe at the rear of the catalytic convertor
(Fig. 12). The downstream heated oxygen sensor
input is used to detect catalytic convertor deteriora-
tion. As the convertor deteriorates, the input from
the downstream sensor begins to match the upstream
sensor input except for a slight time delay. By com-
paring the downstream heated oxygen sensor input
to the input from the upstream sensor, the PCM cal-
culates catalytic convertor efficiency.
IGNITION CIRCUIT SENSE—PCM INPUT
The ignition circuit sense input tells the Power-
train Control Module (PCM) the ignition switch has
energized the ignition circuit. Refer to the wiring dia-
grams for circuit information.
INTAKE AIR TEMPERATURE SENSOR—PCM INPUT
The Intake Air Temperature (IAT) sensor measures
the temperature of the intake air as it enters the
engine. The sensor supplies one of the inputs the
PCM uses to determine injector pulse width and
spark advance.
As Intake Air temperature varies the Intake Air
Temperature sensors resistance changes resulting in
a different input voltage to the PCM.
EXHAUST MANIFOLD OXYGEN SORS SEN- DOWNSTREAM OXYGEN CATALYTIC CON- SENSOR VERTOR
Fig. 12 Downstream Heated Oxygen Sensor
The IAT sensor and Manifold Absolute Pressure
(MAP) switch are a combined into a single sensor
that attachs to the intake manifold (Fig. 13) or (Fig.
14).
INTAKE MANI- FOLD
FUEL RAIL
Fig. 13 / MAP/Intake Air Temperature Sensor—SOHC
Fig. 14 MAP/Intake Air Temperature Sensor—DOHC
PL
PERATURE MAP/AIR SENSOR TEM-