Chrysler PT Cruiser, Service & Repair Manual, Page: 2021 / 2078

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Fuel system in Closed Loop
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Long Term Adaptive (within parameters)
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Power Steering Switch in low PSI (no load)
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Engine at idle
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Fuel level above 15%
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Ambient air temperature
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Barometric pressure
•
Engine RPM within acceptable range of desired
idle
•
Closed throttle speed
Pending Conditions—The Task Manager typi-
cally does not run the Oxygen Sensor Signal Monitor
if overlapping monitors are running or the MIL is
illuminated for any of the following:
•
Misfire Monitor
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Front Oxygen Sensor and Heater Monitor
•
MAP Sensor
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Vehicle Speed Sensor
•
Engine Coolant Temperature Sensor
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Throttle Position Sensor
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Engine Controller Self Test Faults
•
Cam or Crank Sensor
•
Injector and Coil
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Idle Air Control Motor
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EVAP Electrical
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EGR Solenoid Electrical
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Intake Air Temperature
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5 Volt Feed
Conflict—The Task Manager does not run the
Oxygen Sensor Monitor if any of the following condi-
tions are present:
•
A/C ON (A/C clutch cycling temporarily sus-
pends monitor)
•
Purge flow in progress
•
Ethenal content learn is taking place and the
ethenal used once flag is set
Suspend—The Task Manager suspends maturing
a fault for the Oxygen Sensor Monitor if an of the fol-
lowing are present:
•
Oxygen Sensor Heater Monitor, Priority 1
•
Misfire Monitor, Priority 2
OXYGEN SENSOR HEATER MONITOR (NGC)
DESCRIPTION—If the Oxygen sensor (O2S) DTC
as well as a O2S heater DTC is present, the O2S
Heater DTC MUST be repaired first. After the O2S
Heater is repaired, verify that the sensor circuit is
operating correctly.
The voltage reading taken from the O2S are very
temperature sensitive. The readings taken from the
O2S are not accurate below 300 degrees C. Heating
the O2S is done to allow the engine controller to shift
to closed loop control as soon as possible. The heating
element used to heat the O2S must be tested to
ensure that it is heating the sensor properly. Starting
with the introduction on the NGC module the strat-
egy for checking the heater circuit has changed. The
heater resistance is checked by the NGC almost
immediately after the engine is started. The same
O2S heater return pin used to read the heater resis-
tance is capable of detecting an open circuit, a
shorted high or shorted low condition.
OXYGEN SENSOR HEATER MONITOR (SBEC)
DESCRIPTION—If there is an oxygen sensor
(O2S) DTC as well as a O2S heater DTC, the O2S
heater fault MUST be repaired first. After the O2S
fault is repaired, verify that the heater circuit is
operating correctly.
The voltage readings taken from the O2S are very
temperature sensitive. The readings are not accurate
below 300°C. Heating of the O2S is done to allow the
engine controller to shift to closed loop control as
soon as possible. The heating element used to heat
the O2S must be tested to ensure that it is heating
the sensor properly.
The heater element itself is not tested directly. The
sensor output is used to test the heater by isolating
the effect of the heater element on the O2S output
voltage from the other effects. The resistance is nor-
mally between 100 ohms and 4.5 megaohms. When
oxygen sensor temperature increases, the resistance
in the internal circuit decreases. The PCM sends a 5
volts biased signal through the oxygen sensors to
ground this monitoring circuit. As the temperature
increases, resistance decreases and the PCM detects
a lower voltage at the reference signal. Inversely, as
the temperature decreases, the resistance increases
and the PCM detects a higher voltage at the refer-
ence signal. The O2S circuit is monitored for a drop
in voltage.
OPERATION—The Oxygen Sensor Heater Moni-
tor begins after the ignition has been turned OFF
and the O2 sensors have cooled. The PCM sends a 5
volt bias to the oxygen sensor every 1.6 seconds. The
PCM keeps it biased for 35 ms each time. As the sen-
sor cools down, the resistance increases and the PCM
reads the increase in voltage. Once voltage has
increased to a predetermined amount, higher than
when the test started, the oxygen sensor is cool
enough to test heater operation.
When the oxygen sensor is cool enough, the PCM
energizes the ASD relay. Voltage to the O2 sensor
begins to increase the temperature. As the sensor
temperature
increases, the internal resistance
decreases. The PCM continues biasing the 5 volt sig-
nal to the sensor. Each time the signal is biased, the
PCM reads a voltage decrease. When the PCM
detects a voltage decrease of a predetermined value
for several biased pulses, the test passes.
PT
EMISSIONS CONTROL 25 - 3
EMISSIONS CONTROL (Continued)