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Home >> Dodge or Ram Truck >> 2001 >> Durango 4WD V8-4.7L VIN N >> Repair and Diagnosis >> Powertrain Management >> Transmission Control Systems >> Relays and Modules - Transmission and Drivetrain >> Relays and Modules - Transfer Case >> Control Module >> Description and Operation

Control Module: Description and Operation

Fig. 15 Transfer Case Control Module (TCCM):




The Transfer Case Control Module (TCCM) (Fig. 15) is a microprocessor-based assembly, controlling the 4X4 transfer case shift functions via the actuation of a shift motor and utilizing the feedback of a mode sensor assembly. Communication is via the PCI serial bus. Inputs include user selectable 4X4 modes that include AWD(NV244), 2WD(NV233), 4HI, 4L0, and Neutral. The logic and driver circuitry is contained in a molded plastic housing with an embedded heat-sink and is located behind the center section of the lower instrument panel, to the right of the steering column.

The Transfer Case Control Module (TCCM) utilizes the input from the transfer case mounted mode sensor, the instrument panel mounted selector switch, and the following information from the vehicle's PCI serial bus to determine if a shift is allowed.
- Engine RPM and Vehicle Speed
- Diagnostic Requests
- Manual Transmission and Brake Applied
- PRNDL
- Ignition Status
- VIN

Once the TCCM 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 TCCM 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 TCCM has recognized a fault (DTC) of some variety, it will begin operation in one of four Functionality Levels. These levels are:
- Level Zero - Normal Operation.
- Level One - Only Mode Shifts Are Allowed.
- Level Two - Only Mode Shifts and Shifts Into LOW Are Allowed (No Neutral Shifts Are Allowed).
- Level Three - No Shifts Are Allowed

The TCCM can also be operating in one of three possible power modes. These power modes are:
- Full Power Mode is the normal operational mode of the module. This mode is achieved by normal PCI bus traffic being present and the ignition being in the RUN position.
- 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 oft, 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.Sleep Mode will be entered, from the Reduced Power Mode, when no PCI traffic has been sensed for 20 ± 1 seconds. If during Sleep Mode the module detects PCI 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 TCCM is in full power mode and at functionality level zero, it uses the following criteria to determine if a shift is allowed.
Mode shifts will be allowed regardless of transmission gear or vehicle speed, whenever the following conditions are met:
- A change in the Selector switch state indicates that a mode shift has been requested.
- A valid mode sensor signal is being sensed by the TCCM.
- Proper transmit/receive messages are occurring on the PCI bus.
- Ignition key switch is in the RUN position.

Range shifts will be allowed only if all of the following conditions are met:
- A change in the Selector Switch state indicating a range shift has been requested.
- Transmission in NEUTRAL signal must be recognized for at least 1.5 seconds ± 100 msec.
- Proper transmit/receive messages are occurring on the PCI bus.
- Clutch signal is recognized for 500 msec ± 50 msec (Clutch pedal depressed if a manual transmission).
- Vehicle speed is less than or equal to 4.8 Kph (3 mph).
- Ignition key switch is in the RUN position.
- A valid mode sensor signal is being sensed by the TCCM.

A shift into transfer case Neutral will be allowed only if all of the following conditions are met:
- The recessed Neutral Selection switch has been depressed continuously for 4.0 seconds ± 100 msec while all shift conditions have been continuously met.
- Transmission in NEUTRAL signal recognized from the bus.
- Clutch signal is recognized from the bus (Clutch pedal depressed if a manual transmission).
- Proper message transmissions/receptions are occurring on the PCI bus.
- Vehicle speed is less than or equal to 4.8 Kph (3 mph).
- Ignition key switch is in the RUN position, engine OFF.
- Foot Brake is applied.
- A valid mode sensor signal is being sensed by the TCCM.

A shift out of transfer case Neutral will be allowed only if all of the following conditions are met:
- The recessed Neutral Selection switch has been depressed continuously for 1.0 seconds ± 100 msec while all shift conditions have been continuously met.
- Transmission in NEUTRAL signal recognized from the bus.
- Clutch signal is recognized from the bus (Clutch pedal depressed if a manual transmission).
- Proper message transmissions/receptions are occurring on the PCI bus.
- Vehicle speed is less than or equal to 4.8 Kph (3 mph).
- Ignition key switch is in the RUN position, engine OFF.
- Foot Brake is applied.
- A valid mode sensor signal is being sensed by the TCCM.

Shift Sequences
Once all the driver controllable conditions for the requested shift have been met, the TCCM begins a shift timer with a maximum duration of 1 second. If the shift timer expires before the TCCM recognizes to correct mode sensor code, the shift is considered to have been blocked. The blocked shift will increment the blocked shift counter by one. The TCCM strategy for handling blocked shifts will be described later. The process the TCCM performs for the various shifts will be described first.

Range And Mode Shifts
The process for performing all the range and mode shifts are the same. The following steps describe the process.
- Allow time for Selector Switch debounce; 250 msec ± 250 msec.
- Perform diagnostics on the motor that will check for opens/shorts.
- Engage the shift motor for a maximum of 1 second ± 100 msec per 'D' channel transition in the destination gear's direction while monitoring the mode sensor channel transitions.
- Transmit a bus message that a transfer case shift is in progress.
- Disengage the shift motor when the correct mode sensor code is recognized.
- Solidly illuminate the current transfer case position's LED while extinguishing the source gear's LED.
- Transmit a bus message that the transfer case shift is complete.
- If the desired mode sensor code is not received after the shift timer expires (i.e. a blocked or other condition exists), stop driving the motor and wait for 1.5 sec ± 50 msec. The shift motor is then reversed in the direction back toward the source gear for up to 0.7 seconds ± 100msec. The TCCM waits for 1.5 sec ± 50 msec. and repeats the attempt to shift to the desired position.

Shift Out Of Neutral
- Perform diagnostics on the motor that will check for opens/shorts.
- Transmit a bus message that a transfer case shift is in progress.
- Engage the shift motor for a maximum of 1 second ± 100 msec toward the transfer case 4H mode position while monitoring the mode sensor channel transitions.
- Disengage the shift motor when the correct mode sensor code is recognized.
- Extinguish the Neutral LED.
- Transmit a bus message that the transfer case shift is complete.
- If the desired mode sensor code is not received after the shift timer expires (i.e. a blocked or other condition exists), stop driving the motor and wait for 1.5 sec ± 5O msec. The shift motor is then reversed in the direction back toward the source gear for up to 0.7 seconds ± 100msec. The TCCM waits for 1.5 sec ± 50 msec. and repeats the attempt to shift to the desired position.
- When the Neutral button is released, if the 4H position is the desired position, the shift is complete. Illuminate the 4H LED.
- Otherwise when the Neutral button is released, if all of the shift requirements are being met then engage the shift motor towards the desired position for 1 second ± 100 msec per 'D' channel. (if requirements for shifting are not met, illuminate the 4H LED and flash the destination LED as an indication to the driver that all of the driver controllable shift conditions are not being met) If this requires another range or mode shift, begin the range/mode shift process.
- If the desired mode sensor code is not received after the shift timer expires (i.e. a blocked or other condition exists), refer to the Blocked Shift Strategy.

Blocked Shift Strategy
When a shift is commanded, the shift motor will be driven towards its destination position, except in the case of shifting out of Neutral if 4L was selected (the transfer case will shift to the 4H position first, before proceeding to 4L). If the shift is blocked on the way to the destination, the TCCM attempts to drive the motor back to the original position. This process will be allowed to occur 5 times before the system stops trying to achieve the desired position. To re-attempt the desired shift, the selector switch will need to be rotated back to the original position until the switch debounce timer expires then a shift will need to be requested again. The TCCM will not prevent shifts on the basis of a block in the destination direction

If the mode sensor position at the end of the 5th blocked attempt is at any other between gear code, drive the shift motor towards the 4H position.

For all blocked shifts in one direction or both directions (destination gear and reversal target), the status of the driver controllable conditions are always rechecked at the end of the reversal unless the mode sensor is still in the Neutral region (actual position or the between gears position on either side). If the mode sensor is in the Neutral region at the expiration of the shift timer, the TCCM will continue to make the shift attempts according to the blocked shift strategy independent of whether or not the driver controlled conditions are met.

For shifts out of Neutral, if all 5 attempts fail to reach the desired position (which by default is 4H) then the motor will be driven to stall in the 4H direction. After the 2 second ± 100 msec drive/stall, the TCCM will look at mode sensor position. In the worst case situation after the 2 second drive/stall operation, if the shift motor cannot get to the between gears position on the Neutral side of 4H, the unit will still be considered to be in Neutral. The Neutral LED and 'Service 4WD' lamp will be illuminated. Otherwise the motor will be on the correct side of the rooster comb and the system will depend on the shift detent poppet to center the sector.

Shift Reversal Targets
If the shift timer expires (1 second per 'D' channel) and we have not made the desired position, all shifts will attempt to return to their original position with the exceptions of:
- If the intended shift is going to the High rail from Low and can't make it, but it can make the 2WD/4WD position, we stop at that position. The TCCM will not attempt to cross back over Neutral if it does not have to. This means that there was a block on the first attempt to go to 4H and the transfer case has made it through Neutral to a known good channel, then the motor will go back only to the 2WD/4WD position and execute the remainder of the attempts from there.
- For shifts out of Neutral, any time a shift is commanded out of Neutral the system needs to get out. The same scenario of attempting to get out of Neutral and then returning to it should be followed for all of the shift attempts. The only exception is a shift out of Neutral towards the high side can be considered complete if it can make a between gears reading for the nearest high position. The TCCM should never go to Neutral unless the driver is commanding it and all required conditions are being met

Shift Attempt Limit
To protect the transfer case system, the TCCM will impose a limit on the number of shifts that can occur over a calibrated time period. The system will monitor the number of 'D' channel segment transitions that occur in any 30 second time period. If the number of segment transitions is 30 or greater, the system will go into a default mode. The default mode of operation for shifting is that the number of allowed 'D' channel transitions permitted to occur will be 3 over each 15 second ± 100 msec calibrated window of time. After 5 minutes ± 100 msec, the motor can be assumed to have cooled down and the system will revert to normal operation. The following rules also apply to the shift limit:
- The attempt limit will not include shifts coming out of Neutral, they will be allowed regardless of the counter/timer.
- Any shift that is in progress when the counter reaches a maximum count in time will be allowed to complete before the default mode is entered. D-channel transitions during this period will not be counted towards the default mode limit.
- A block, regardless of the direction, whether towards destination or back towards reversal target (shift timer expiring), will count as a value of 2 transitions towards the 30 segment transitions to go into default mode as defined above. Current attempt limit values are 30 transitions in 30 seconds and default mode values are 3 transitions every 15 seconds for 5 minutes.
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