Chrysler 1998 Viper RT/10 Owner's Manual page 929

S R
EMISSION CONTROL SYSTEMS 25 - 7
D E S C R I P T I O N A N D O P E R A T I O N ( C o n t i n u e d )
element of the feedback system is the 0 2 S . The 02S
is located i n the exhaust path. Once i t reaches oper-
ating temperature 300° to 350°C (572° to 662°F), the
sensor generates a voltage that is inversely propor-
tional to the amount of oxygen i n the exhaust. The
information obtained by the sensor is used to calcu-
late the fuel injector pulse w i d t h . This maintains a
14.7 to 1 A i r Fuel (A/F) ratio. A t this m i x t u r e ratio,
the catalyst works best to remove hydrocarbons ( H C ) ,
carbon monoxide ( C O ) and nitrogen oxide (NOx) from
the exhaust.
The 0 2 S is also the m a i n sensing element for the
EGR, Catalyst and Fuel Monitors.
The 0 2 S can fail i n any or all of the following
manners;
• Slow response rate
• Reduced output voltage
• Dynamic shift
• Shorted or open circuits
Response rate is the time required for the sensor to
switch from lean to rich once i t is exposed to a richer
t h a n o p t i m u m A/F m i x t u r e or vice versa. As the sen-
sor starts malfunctioning, i t could take longer to
detect the changes i n the oxygen content of the
exhaust gas.
The output voltage of the 02S ranges from 0 to 1
volt. A good sensor can easily generate any output
voltage i n this range as i t is exposed to different con-
centrations of oxygen. To detect a shift i n the A / F
mixture (lean or rich), the output voltage has to
change beyond a threshold value. A malfunctioning
sensor could have difficulty changing beyond the
threshold value.
DTC
21
—OXYGEN
SENSOR HEATER MONITOR
I f there is an oxygen sensor (02S) DTC as w e l l as
a 02S heater DTC, the 0 2 S fault M U S T be repaired
first. After the 0 2 S fault is repaired, verify t h a t the
heater circuit is operating correctly.
Effective control of exhaust emissions is achieved
by an oxygen feedback system. The most i m p o r t a n t
element of the feedback system is the 02S. The 02S
is located i n the exhaust path. Once i t reaches oper-
ating temperature 300° to 350°C (572 °to 662°F), the
sensor generates a voltage t h a t is inversely propor-
tional to the amount of oxygen i n the exhaust. The
information obtained by the sensor is used to calcu-
late the fuel injector pulse w i d t h . This maintains a
14.7 to 1 A i r Fuel (A/F) ratio. A t this m i x t u r e ratio,
the catalyst works best to remove hydrocarbons (HC),
carbon monoxide (CO) and nitrogen oxide (NOx) from
the exhaust.
The voltage readings taken from the 0 2 S sensor
are very temperature sensitive. The readings are not
accurate below 300°C. Heating of the 0 2 S sensor is
done to allow the engine controller to shift to closed
loop control as soon as possible. The heating element
used to heat the 02S sensor must be tested to ensure
t h a t i t is heating the sensor properly.
The 02S sensor circuit is monitored for a drop i n
voltage d u r i n g w a r m u p of the sensor. The sensor out-
p u t is used to test the heater by isolating the effect
of the heater element on the 0 2 S sensor output volt-
age from the other effects.
DTC 51/52—FUEL SYSTEM MONITOR
To comply w i t h clean air regulations, vehicles are
equipped w i t h catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide. The catalyst works best
when the A i r Fuel (A/F) ratio is at or near the opti-
m u m of 14.7 to 1.
The P C M is programmed to m a i n t a i n the o p t i m u m
air/fuel ratio of 14.7 to 1. This is done by m a k i n g
short t e r m corrections i n the fuel injector pulse w i d t h
based on the 0 2 S sensor output. The programmed
memory acts as a self calibration tool t h a t the engine
controller uses to compensate for variations i n engine
specifications, sensor tolerances and engine fatigue
over the life span of the engine. B y monitoring the
actual fuel-air ratio w i t h the 0 2 S sensor (short term)
and m u l t i p l y i n g t h a t w i t h the program long-term
(adaptive) memory and comparing t h a t to the l i m i t ,
i t can be determined whether i t w i l l pass an emis-
sions test. I f a malfunction occurs such t h a t the P C M
cannot m a i n t a i n the o p t i m u m A / F ratio, then the
M I L w i l l be illuminated.
DTC 64—CATALYST MONITOR
To comply w i t h clean air regulations, vehicles are
equipped w i t h catalytic converters. These converters
reduce the emission of hydrocarbons, oxides of nitro-
gen and carbon monoxide.
N o r m a l vehicle miles or engine misfire can cause a
catalyst to decay. A meltdown of the ceramic core can
cause a reduction of the exhaust passage. This can
increase vehicle emissions and deteriorate engine
performance, drive ability and fuel economy.
The catalyst monitor uses dual oxygen sensors
(02S's) to monitor the efficiency of the converter. The
dual 02S's sensor strategy is based on the fact that
as a catalyst deteriorates, its oxygen storage capacity
and its efficiency are both reduced. By monitoring
the oxygen storage capacity of a catalyst, its effi-
ciency can be indirectly calculated. The upstream
0 2 S is used to detect the amount of oxygen i n the
exhaust gas before the gas enters the catalytic con-
verter. The P C M calculates the A / F m i x t u r e from the
output of the 02S. A low voltage indicates h i g h oxy-
gen content (lean mixture). A h i g h voltage indicates a
low content of oxygen (rich mixture).
When the upstream 02S detects a lean condition,
there is an abundance of oxygen i n the exhaust gas.
A functioning converter would store this oxygen so i t