Chrysler Stratus RHD 1999 Electronic Service Manual page 958

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DESCRIPTION AND OPERATION (Continued)
instrument panel). Also, the PCM stores an engine
misfire DTC in memory.
The PCM performs several diagnostic routines.
They include:
• Oxygen sensor monitor
• Downstream heated oxygen sensor diagnostics
during open loop operation (except for shorted)
• Fuel system monitor
• EGR monitor
• Purge system monitor
• All inputs monitored for proper voltage range.
• All monitored components (refer to the Emission
section for On-Board Diagnostics).
The PCM compares the upstream and downstream
heated oxygen sensor inputs to measure catalytic
convertor efficiency. If the catalyst efficiency drops
below the minimum acceptable percentage, the PCM
stores a diagnostic trouble code in memory.
During certain idle conditions, the PCM may enter
a variable idle speed strategy. During variable idle
speed strategy the PCM adjusts engine speed based
on the following inputs.
• A/C sense
• Battery voltage
• Battery temperature
• Engine coolant temperature
• Engine run time
• Power steering pressure switch
• Vehicle mileage
ACCELERATION MODE
This is a CLOSED LOOP mode. The PCM recog-
nizes an abrupt increase in Throttle Position sensor
output voltage or MAP sensor output voltage as a
demand for increased engine output and vehicle
acceleration. The PCM increases injector pulse width
in response to increased fuel demand.
DECELERATION MODE
This is a CLOSED LOOP mode. During decelera-
tion the following inputs are received by the PCM:
• A/C pressure transducer
• A/C sense
• Battery voltage
• Intake air temperature
• Engine coolant temperature
• Crankshaft position (engine speed)
• Exhaust gas oxygen content (upstream heated
oxygen sensor)
• Knock sensor
• Manifold absolute pressure
• Power steering pressure switch
• Throttle position
• IAC motor control changes in response to MAP
sensor feedback
The PCM may receive a closed throttle input from
the Throttle Position Sensor (TPS) when it senses an
abrupt decrease in manifold pressure. This indicates
a hard deceleration. In response, the PCM may
momentarily turn off the injectors. This helps
improve fuel economy, emissions and engine braking.
If decel fuel shutoff is detected, downstream oxy-
gen sensor diagnostics is performed.
WIDE-OPEN-THROTTLE MODE
This is an OPEN LOOP mode. During wide-open-
throttle operation, the following inputs are received
by the PCM:
• Intake air temperature
• Engine coolant temperature
• Engine speed
• Knock sensor
• Manifold absolute pressure
• Throttle position
When the PCM senses a wide-open-throttle condi-
tion through the Throttle Position Sensor (TPS) it de-
energizes the A/C compressor clutch relay. This
disables the air conditioning system.
The PCM does not monitor the heated oxygen sen-
sor inputs during wide-open-throttle operation except
for downstream heated oxygen sensor and both
shorted diagnostics. The PCM adjusts injector pulse
width to supply a predetermined amount of addi-
tional fuel.
IGNITION SWITCH OFF MODE
When the operator turns the ignition switch to the
OFF position, the following occurs:
• All outputs are turned off, unless 02 Heater
Monitor test is being run. Refer to the Emission sec-
tion for On-Board Diagnostics.
• No inputs are monitored except for the heated
oxygen sensors. The PCM monitors the heating ele-
ments in the oxygen sensors and then shuts down.
SYSTEM DIAGNOSIS
OPERATION
The PCM can test many of its own input and out-
put circuits. If the PCM senses a fault in a major
system, the PCM stores a Diagnostic Trouble Code
(DTC) in memory.
For DTC information see On-Board Diagnostics.
POWER DISTRIBUTION CENTER
DESCRIPTION
The Power Distribution Center (PDC) is located
next to the PCM (Fig. 1).
FUEL SYSTEM 14 - 29