Chrysler 300M 2002 Service Manual page 1741

GENERAL INFORMATION
Modulated (PWM) output signal. The desired duty
cycle of the PWM is selected from a calibration table
internal to the Body Control Module (BCM).
To obtain the desired solenoid current the duty
cycle of the solenoid can be compensated according
to a current measuring feedback circuit. The speed
proportional steering system is always active with
the ignition on.
The 500Hz PWM output signal is capable of
generating a duty cycle from 0% (full off - minimum
steering assist) to approximately 50% duty cycle
(full on - maximum steering assist) in small incre-
ments. The duty cycle is determined by vehicle
speed and is continuously modified by solenoid
current feedback information. With the engine run-
ning and vehicle speed between 0 km/h (0 mph) and
approximately 32 km/h (20 mph) the duty cycle will
be about 50%. Between approximately 32 km/h (20
mph) and 100 km/h (60 mph) the duty cycle will
gradually decrease to 0% based upon vehicle speed.
Above approximately 100 km/h (60 mph) there is no
assist provided by the speed proportional steering
system. Maximum solenoid current will be limited
to one amp but the system operates at about 0.5
amp. Speed Proportional Steering Solenoid resis-
tance is 5.7-6.3 ohms at 20° C (68° F).
The Speed Proportional Steering System can de-
tect three failure modes relating to the Speed Pro-
portional Steering PWM driver located in the BCM.
If any DTC is set, the solenoid is shut off, unless the
condition goes away before approximately 10 sec-
onds. Once the DTC is set, the solenoid will remain
off for the remainder of the ignition cycle.
1. An open or shorted to ground circuit fault is
detected by monitoring the feedback circuit. If
the BCM detects that the feedback circuit has
zero current when the software indicates the
solenoid circuit should have current, the DTC
will be set. This test is performed every 250
milliseconds.
2. A short to voltage fault is detected by monitoring
the feedback circuit. The DTC will be set when
the BCM has sensed that there was current on
the solenoid feedback circuit when the solenoid
was turned off.
3. An over temperature or thermal shutdown DTC
will be set by default if the internal diagnostic
pin of the solenoid driver is at a low level, but the
feedback measurement does not show a high
PWM output current.
3.16 VEHICLE COMMUNICATION
The Programmable Communication Interface or
PCI Bus is a single wire multiplexed network capa-
ble of supporting binary encoded messages shared
between multiple modules. The PCI bus circuit is
identified as D25. The modules are wired in paral-
lel. Connections are made through the BCM. The
BCM acts as a splice to connect each module and
the Data Link Connector (DLC) together. The fol-
lowing modules are used on 2002 LH:
• Airbag Control Module
• Left Side Impact Airbag Control Module
•
Right Side Impact Airbag Control Module
• Controller Antilock Brake
• Powertrain Control Module - Next Generation
Controller (NGC)
•
Radio (If equipped)
• CD Changer (If equipped)
• Overhead Travel
equipped)
•
Memory Heated Seat and Memory Mirror (If
equipped)
• Automatic Temperature Control (If equipped)
•
Body Control Module
• Sentry Key Immobilizer Module (If equipped)
• Mechanical Instrument Cluster
Each module provides its own bias and termina-
tion in order to transmit and receive messages. The
bus voltage is at zero volts when no modules are
transmitting and is pulled up to about seven and a
half volts when modules are transmitting.
The bus messages are transmitted at a rate
averaging 10800 bits per second. Since there is only
voltage present when the modules transmit and the
message length is only about 500 milliseconds, it is
ineffective to try and measure the bus activity with
a conventional voltmeter. The preferred method is
to use the DRBIII lab scope. The 12v square wave
selection on the 20-volt scale provides a good view of
the bus activity. Voltage on the bus should pulse
between zero and about seven and half volts. Refer
to the following figure for some typical displays.
The PCI Bus failure modes are broken down into
two categories. Complete PCI Bus Communication
Failure and individual module to response. Causes
of a complete PCI Bus Communication Failure
include a short to ground or battery on the PCI
circuit. Individual module no response can be
caused by an open circuit at the BCM or at the
module, or an open battery or ground circuit to the
affected module.
Symptoms of a complete PCI Bus Communication
Failure would include but are not limited to:
•
All gauges on the EMIC stay at zero
• All telltales on EMIC illuminate
• EMIC backlighting at full intensity
•
No response received from any module on the PCI
bus (except PCM)
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Information System (If