Dakota 4WD V8-4.7L Flex Fuel (2008)
Control Module: Description and Operation
Operation
OPERATION
The Front Control Module (FCM) utilizes the input from the transfer case mounted mode sensor, the instrument panel mounted selector switch, and the
following information from the vehicle's CAN bus to determine if a shift is allowed.
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Engine RPM and Vehicle Speed
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Diagnostic Requests
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Manual Transmission Clutch Switch
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Brake Applied
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PRNDL
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Ignition Status
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ABS Messages
Once the FCM determines that a requested shift is allowed, it actuates the bi-directional shift motor as necessary to achieve the desired transfer case
operating mode. The FCM also monitors the mode sensor while controlling the shift motor to determine the status of the shift attempt.
Several items can cause the requested shift not to be completed. If the FCM has recognized a fault (DTC) of some variety, it will begin operation in one
of four Functionality Levels. These levels are:
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Level Zero - Normal Operation.
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Level One - Only Mode Shifts Are Allowed.
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Level Two - Only Mode Shifts and Shifts Into LOW Are Allowed (No Neutral Shifts Are Allowed).
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Level Three - No Shifts Are Allowed
The FCM can also be operating in one of three possible power modes. These power modes are:
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Full Power Mode is the normal operational mode of the module. This mode is achieved by normal CAN bus traffic being present and the ignition
being in the RUN position.
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Reduced Power Mode will be entered when the ignition has been powered off. In this state, the module will shut down power supplied to
external devices, and to electronic interface inputs and outputs. From this state the module can enter either Sleep Mode or Full Power Mode. To
enter this mode, the module must receive an ignition message denoting that the ignition is off, or not receive any messages for 5 ±0.5 seconds. To
exit this mode, the module must receive one ignition message that denotes that the ignition is in the RUN position.
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Sleep Mode will be entered, from the Reduced Power Mode, when no CAN traffic has been sensed for 20 ±1 seconds. If during Sleep Mode the
module detects CAN bus traffic, it will revert to the Reduced Power mode while monitoring for ignition messages. It will remain in this state as
long as there is traffic other than run or start messages, and will return to Sleep mode if the bus goes without traffic for 20 ±1 seconds.
SHIFT REQUIREMENTS
If the FCM is in full power mode and at functionality level zero, it uses the following criteria to determine if a shift is allowed.
If any of the driver controllable conditions are not met once the shift request is recognized, the FCM may illuminate one or more of the 4WD system
message icons in the instrument cluster display.
Mode shifts will be allowed regardless of transmission gear or vehicle speed, whenever the following conditions are met:
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Ignition key switch is in the RUN position.
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Front and rear wheel speed are within 21 km/hr (13 mph).
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A change in the Selector switch state indicates that a mode shift has been requested.
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A valid mode sensor signal is being sensed by the FCM.
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Proper transmit/receive messages are occurring on the CAN bus.
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An Anti-lock Brake System (ABS) event is not in progress.
Range shifts will be allowed only if all of the following conditions are met:
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Ignition key switch is in the RUN position.
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Front and rear wheel speed are within 21 km/hr (13 mph).
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A change in the Selector Switch state indicating a range shift has been requested.
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Transmission in NEUTRAL signal must be recognized for at least 1.5 seconds ±100 msec. (Automatic transmissions only)
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Proper transmit/receive messages are occurring on the CAN bus.
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Clutch signal is recognized for 500 msec ± 50 msec (Manual transmissions only).
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Vehicle speed is less than or equal to 4.8 km/hr (3 miles per hour).
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A valid mode sensor signal is being sensed by the FCM.
