Grand Caravan FWD V6-3.8L VIN L (2001)
SENSOR RETURN - PCM INPUT
The sensor return circuit provides a low electrical noise ground reference for all of the systems sensors. The sensor return circuit connects to
internal ground circuits within the Powertrain Control Module (PCM).
SCI RECEIVE - PCM INPUT
SCI Receive is the serial data communication receive circuit for the DRB scan tool. The Powertrain Control Module (PCM) receives data from the
DRB through the SCI Receive circuit.
IGNITION SENSE - PCM INPUT
The ignition sense input informs the Powertrain Control Module (PCM) that the ignition switch is in the crank or run position.
PCM GROUND
Ground is provided through multiple pins of the PCM connector. Depending on the vehicle there may be as many as three different ground pins.
There are power grounds and sensor grounds.
The power grounds are used to control the ground side of any relay, solenoid, ignition coil or injector. The signal ground is used for any input that
uses sensor return for ground, and the ground side of any internal processing component.
The SBEC III case is shielded to prevent RFI and EMI. The PCM case is grounded and must be firmly attached to a good, clean body ground.
Internally all grounds are connected together, however there is noise suppression on the sensor ground. For EMI and RFI protection the case is
also grounded separately from the ground pins.
8 VOLT SUPPLY - PCM OUTPUT
The PCM supplies 8 volts to the crankshaft position sensor, camshaft position sensor.
5 VOLT SUPPLY - PCM OUTPUT
The PCM supplies 5 volts to the following sensors:
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A/C pressure transducer
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Engine coolant temperature sensor
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Manifold absolute pressure sensor
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Throttle position sensor
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Linear EGR solenoid
MODES OF OPERATION
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 (WOT). There are several different modes of operation that determine
how the PCM responds to the various input signals.
There are two different areas of operation, OPEN LOOP and CLOSED LOOP.
During OPEN LOOP modes the PCM receives input signals and responds according to preset PCM programming. Inputs from the upstream and
down- stream heated oxygen sensors are not monitored during OPEN LOOP modes, except for heated oxygen sensor diagnostics (they are
checked for shorted conditions at all times).
During CLOSED LOOP modes the PCM monitors the inputs from the upstream and downstream heated oxygen sensors. The upstream heated
oxygen sensor input tells the PCM if the calculated injector pulse width resulted in the ideal air-fuel ratio of 14.7 to one. By monitoring the
exhaust oxygen content through the upstream heated oxygen sensor, the PCM can fine tune injector pulse width. Fine tuning injector pulse width
allows the PCM to achieve optimum fuel economy combined with low emissions.
For the PCM to enter CLOSED LOOP operation, the following must occur:
1. Engine coolant temperature must be over 35 °F.
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If the coolant is over 35 °F the PCM will wait 44 seconds.
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If the coolant is over 50 °F the PCM will wait 38 seconds.
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If the coolant is over 167 °F the PCM will wait 11 seconds.
2. For other temperatures the PCM will interpolate the correct waiting time.
3. O2 sensor must read. either greater than 0.745 volts or less than 0.1 volt.
4. The multi-port fuel injection systems has the following modes of operation:
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Ignition switch ON (Zero RPM)
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Engine start-up
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Engine warm-up
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Cruise
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Idle
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Acceleration
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Deceleration
