Chrysler Concorde 1993 Service Manual page 516

SCI CIRCUITS
The powertrain control module (PCM) communi-
cates with the DRB II scan tool through the serial
communication interface (SCI) receive and transmit
circuits. Technicians can connect the DRB II scan
tool to the data link connector. The data link connec-
tor contains 6 terminals. Terminal 3 is the SCI Re-
ceive circuit. Terminal 4 is the SCI Transmit circuit.
AIR CONDITIONING PRESSURE
TRANSDUCER—PCM INPUT
The powertrain control module (PCM) monitors the
A/C compressor discharge
through the air conditioning pressure transducer.
The transducer supplies an input to the PCM. The
PCM engages the A/C compressor clutch if pressure
is sufficient for A/C system operation.
ASD SENSE—PCM INPUT
The automatic shutdown (ASD) sense circuit in-
forms the powertrain control module when the ASD
relay contacts close. When energized, the ASD relay
supplies battery voltage to the fuel injectors and ig-
nition coils.
BATTERY VOLTAGE—PCM INPUT
The PCM monitors the battery voltage input to de-
termine fuel injector pulse width and generator field
control. If battery voltage is low, the PCM increases
injector pulse width (period of time that the injector
is energized).
BRAKE SWITCH—PCM INPUT
When the operator applies the brakes, the power-
train control module (PCM) receives an input from
the brake switch. When the PCM receives the brake
switch input a closed throttle input from the throttle
position sensor simultaneously, it recognizes a decel-
eration condition. The PCM adjusts injector pulse
width to compensate for the deceleration condition.
If the PCM receives a brake switch input while the
speed control system is operating, the PCM disables
the speed control system.
CAMSHAFT POSITION SENSOR—PCM INPUT
The camshaft position sensor provides cylinder
identification to the powertrain control module
(PCM) (Fig. 3 or Fig. 4). The sensor generates pulses
as groups of notches on the camshaft sprocket pass
underneath it (Fig. 5 or Fig. 6). The PCM keeps
track of crankshaft rotation and identifies each cyl-
inder by the pulses generated by the notches on the
camshaft sprocket. Four crankshaft pulses follow
each group of camshaft pulses.
When the PCM receives two cam pulses followed
by the long flat spot on the camshaft sprocket, it
knows that the crankshaft timing marks for cylinder
one are next (on driveplate). When the PCM receives
(high side) pressure
one camshaft pulse after the long flat spot on the
sprocket, cylinder number two crankshaft timing
marks are next. After 3 camshaft pulses, the PCM
knows cylinder four crankshaft timing marks follow.
One camshaft pulse after the three pulses indicates
cylinder five. The two camshaft pulses after cylinder
5 signals cylinder six (Fig. 5 or Fig. 6). The PCM can
synchronize on cylinders 1 or 4.
When metal aligns with the sensor, voltage goes
low (less than 0.3 volts). When a notch aligns with
the sensor, voltage spikes high (5.0 volts). As a group
of notches pass under the sensor, the voltage
switches from low (metal) to high (notch) then back
to low. The number of notches determine the amount
of pulses. If available, an oscilloscope can display the
square wave patterns of each timing events.
Top dead center (TDC) does not occur when notches
on the camshaft sprocket pass below the cylinder.
TDC occurs after the camshaft pulse (or pulses) and
after the 4 crankshaft pulses associated with the par-
ticular cylinder. The arrows and cylinder call outs on
Figures 5 and 6 represent which cylinder the flat
spot and notches identify, they do not indicate TDC
position.
Fig. 3 Camshaft Position Sensor—3.3L Engine
Fig. 4 Camshaft Position Sensor—3.5L Engine
The camshaft position sensor is mounted in the
front of the timing case cover (Fig. 7 or Fig. 8).
CHARGE AIR TEMPERATURE SENSOR—PCM
INPUT
The 3.5L engine uses a charge air temperature sen-
sor, the 3.3L engine does not. The sensor threads into
FUEL SYSTEMS 14 - 23