Chrysler Concorde 2004 Service Manual page 667

3.2.4 PCM OPERATING MODES
As input signals to the PCM change, the PCM
adjusts its response to output devices. For example,
the PCM must calculate a different injector pulse
width and ignition timing for idle than it does for
wide open throttle. There are several different
modes of operation that determine how the PCM
responds to the various input signals.
There are two types of engine control operation:
open loop and closed loop.
In open loop operation, the PCM receives input
signals and responds according to preset program-
ming. Inputs from the heated oxygen sensors are
not monitored.
In closed loop operation, the PCM monitors the
inputs from the heated oxygen sensors. This input
indicates to the PCM whether or not the calculated
injector pulse width results in the ideal air-fuel
ratio of 14.7 parts air to 1 part fuel. By monitoring
the exhaust oxygen content through the oxygen
sensor, the PCM can fine tune injector pulse width.
Fine tuning injector pulse width allows the PCM to
achieve the lowest emission levels while maintain-
ing optimum fuel economy.
The engine start-up (crank), engine warm-up,
and wide open throttle modes are open loop modes.
Under most operating conditions, closed loop modes
occur with the engine at operating temperature.
3.2.5 NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems, and conditions even though they could
have malfunctions that result in driveability prob-
lems. A diagnostic code may not be displayed for the
following conditions. However, problems with these
systems may cause a diagnostic code to be displayed
for other systems. For example, a fuel pressure
problem will not register a diagnostic code directly,
but could cause a rich or lean condition. This could
cause an oxygen sensor, fuel system, or misfire
monitor trouble code to be stored in the PCM.
Engine Timing − The PCM cannot detect an
incorrectly indexed
sprocket, or crankshaft sprocket. The PCM also
cannot detect an incorrectly indexed distributor.(*)
Fuel Pressure − Fuel pressure is controlled by
the fuel pressure regulator. The PCM cannot detect
a clogged fuel pump inlet filter, clogged in-line filter,
or a pinched fuel supply.(*)
Fuel Injectors − The PCM cannot detect if a fuel
injector is clogged, the pintle is sticking, or the
wrong injectors are installed.(*)
Fuel Requirements − Poor quality gasoline can
cause problems such as hard starting, stalling, and
stumble. Use of methanol-gasoline blends may re-
timing chain, camshaft
GENERAL INFORMATION
sult in starting and driveability problems. See indi-
vidual symptoms and their definitions in Section
6.0 (Glossary of Terms).
PCM Grounds − The PCM cannot detect a poor
system ground. However, a diagnostic trouble code
may be stored in the PCM as a result of this
condition.
Throttle Body Air Flow − The PCM cannot
detect a clogged or restricted air cleaner inlet or
filter element.(*)
Exhaust System − The PCM cannot detect a
plugged, restricted, or leaking exhaust system.(*)
Cylinder Compression − The PCM cannot de-
tect uneven, low, or high engine cylinder compres-
sion.(*)
Excessive Oil Consumption − Although the
PCM monitors the exhaust stream oxygen content
through the oxygen sensor when the system is in a
closed loop, it cannot determine excessive oil con-
sumption.
NOTE: Any of these conditions could result
in a rich or lean condition causing an oxygen
sensor TROUBLE CODE to be stored in the
PCM, or the vehicle may exhibit one or more
of the driveability symptoms listed in the
Table of Contents.
3.2.6 SKIS OVERVIEW
The Sentry Key Immobilizer System (SKIS) is
designed to prevent unauthorized vehicle opera-
tion. The system consists of a Sentry Key Immobi-
lizer Module (SKIM), ignition key(s) equipped with
a transponder chip and PCM. When the ignition
switch is turned on, the SKIM interrogates the
ignition key. If the ignition key is Valid or Invalid,
the SKIM sends a PCI Bus message to the PCM
indicating ignition key status. Upon receiving this
message the PCM will terminate engine operation,
or allow the engine to continue to operate.
3.2.7 SKIM ON-BOARD DIAGNOSTICS
The SKIM has been programmed to transmit and
monitor many different coded messages as well as
PCI Bus messages. This monitoring is called On
Board Diagnosis.
Certain criteria must be met for a diagnostic
trouble code to be entered into the SKIM memory.
The criteria may be a range of; Input voltage, PCI
Bus message, or coded messages to the SKIM. If all
of the criteria for monitoring a circuit or function
are met and a fault is sensed, a diagnostic trouble
code will be stored in the SKIM memory.
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