fuel type DODGE NEON 2000 Service User Guide

grammed (fixed) values and inputs from other sen-
sors.
DOWNSTREAM OXYGEN SENSOR 1/2
The Downstream O2 Sensor has two functions.
One function is measuring catalyst efficiency. This is
an OBD II requirement. The oxygen content of theexhaust gasses has significantly less fluctuation than
at the inlet if the converter is working properly. The
PCM compares upstream and Downstream O2 Sen-
sor switch rates under specific operating conditions
to determine if the catalyst is functioning properly.
The other function is a downstream fuel control
which was introduced in 1996. The upstream O2 goal
varies within the window of operation of the O2 Sen-
sor. In the past the goal was a preprogrammed fixed
value based upon where it believed the catalyst oper-
ated most efficiently.
While the Upstream O2 Sensor input is used to
maintain the 14.7:1 air/fuel ratio, variations in
engines, exhaust systems and catalytic converters
may cause this ratio to not be the most ideal for a
particular catalyst and engine. To help maintain the
catalyst operating at maximum efficiency, the PCM
will fine tune the air/fuel ratio entering the catalyst
based upon the oxygen content leaving the catalyst.
This is accomplished by modifying the Upstream O2
Sensor voltage goal.
If the exhaust leaving the catalyst has too much
oxygen (lean ) the PCM increases the upstream O2
goal which increases fuel in the mixture causing less
oxygen to be left over. Conversely, if the oxygen con-
tent leaving the catalyst has is too little oxygen (rich)
the PCM decreases the upstream O2 goal down
which removes fuel from the mixture causing more
oxygen to be left over. This function only occurs dur-
ing downstream closed loop mode operation.
Fig. 13 Heated Oxygen Sensor Systems
1 ± CATALYTIC CONVERTER (LEV EMISSION)
2 ± CLOSE-COUPLED CATALYTIC CONVERTER
(ULEV EMISSION)
3 ± UNDER-FLOOR CATALYTIC CONVERTER
(ULEV EMISSION)
4 ± OXYGEN SENSORS5 ± OXYGEN SENSOR
6 ± CATALYTIC CONVERTER
(FEDERAL EMISSION)
7 ± OXYGEN SENSOR
Fig. 14 Types Of O2 Sensors
1 ± BOSCH
2 ± NEW NTK
3 ± NTK
PLFUEL SYSTEM 14 - 33
DESCRIPTION AND OPERATION (Continued)