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Home >> Dodge and Ram >> 2007 >> RAM 1500 Truck 4WD V8-5.7L VIN D >> Repair and Diagnosis >> Transmission and Drivetrain >> Relays and Modules - Transmission and Drivetrain >> Relays and Modules - Transfer Case >> Control Module >> Description and Operation >> Operation

Operation






OPERATION

The Transfer Case Control Module (TCCM) functionality in the Totally Integrated Power Module (TIPM) 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.

- Engine RPM and Vehicle Speed
- Diagnostic Requests
- Manual Transmission and Brake Applied
- PRNDL
- Ignition Status
- ABS Messages

Once the TIP 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 TIPM 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 TIPM 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 TIPM 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 CAN 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 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.
- 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 TIPM 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 TIPM will solidly illuminate the source position's LED and flash the desired position's LED for all shifts except NEUTRAL. The NEUTRAL shift LED strategy will be discussed later.

Mode shifts will be allowed regardless of transmission gear or vehicle speed, whenever the following conditions are met:

- Front and rear wheel speed are within 21 km/h (13 mph).
- 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 TIPM.
- Proper transmit/receive messages are occurring on the CAN bus.
- Ignition key switch is in the RUN position.

Range shifts will be allowed only if all of the following conditions are met:

- Front and rear wheel speed are within 21 km/h (13 mph).
- 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. (Automatic transmissions only)
- Proper transmit/receive messages are occurring on the CAN bus.
- Clutch signal is recognized for 500 msec ± 50 msec (Manual transmissions only).
- Vehicle speed is less than or equal to 4.8 km/h (3 mph).
- Ignition key switch is in the RUN position.
- A valid mode sensor signal is being sensed by the TIPM.

A shift into transfer case Neutral will be allowed only if all of the following conditions are met:

- Front and rear wheel speed are within 21 km/h (13 mph).
- 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. (Automatic transmissions only)
- Clutch signal is recognized from the bus (Manual transmissions only).
- Proper message transmissions/receptions are occurring on the CAN bus.
- Vehicle speed is less than or equal to 4.8 km/h (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 TIPM.

A shift out of transfer case Neutral will be allowed only if all of the following conditions are met:

- Front and rear wheel speed are within 21 km/h (13 mph).
- 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.(Automatic transmissions only)
- Clutch signal is recognized from the bus (Manual transmissions only).
- Proper message transmissions/receptions are occurring on the CAN bus.
- Vehicle speed is less than or equal to 4.8 km/h (3 mph).
- Ignition key switch is in the RUN position.
- Foot Brake is applied.
- A valid mode sensor signal is being sensed by the TIPM.

SHIFT SEQUENCES

Once all the driver controllable conditions for the requested shift have been met, the TIPM begins a shift timer with a maximum duration of 1 second per 'D' channel transition. If the shift timer expires before the TIPM 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 TIPM strategy for handling blocked shifts will be described later. The process the TIPM 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 ± 50 msec.
- Extinguish the source gear's LED while flashing desired transfer case position's LED.
- 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.
- Disengage the shift motor when the correct mode sensor code is recognized.
- Solidly illuminate the selected 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 (ie. a blocked or other condition exists), stop driving the motor and wait for 200 msec ± 50 msec. The shift motor is then reversed in the direction back toward the source gear for up to 1.0 seconds ± 100 msec. per 'D' channel. The TIPM waits for 2.0 seconds ± 50 msec. and repeats the attempt to shift to the desired position.

The exception to the preceding sequence is when a shift from 4L to 2WD/AWD is requested. If 2WD/AWD is requested from the 4L position, the transfer case is first driven to the 4H position. If the 4H position is reached, the transfer case is then driven back to the 2WD/AWD position and the shift is considered complete. If the transfer case does not reach any the 4H position, but is in the 2WD/AWD 'D' channel, or the 2WD/AWD between gear position on the 4H side of 2WD/AWD, the shift is also considered complete.

SHIFT OUT OF NEUTRAL

The following steps describe the process for a shift out of NEUTRAL.

- Extinguish the Neutral LED.
- 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 (ie. a blocked or other condition exists), stop driving the motor and wait for 200 msec ± 50 msec. The shift motor is then reversed in the direction back toward the source gear for up to 1.0 seconds 100 msec. The TIPM waits for 2.0 seconds ± 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 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 TIPM may attempt to drive the motor back to the original position. This process will be allowed to occur 5 times. If the transfer case has reached a non-NEUTRAL 'D' channel during the shift re-attempts, the LED for the achieved gear position is illuminated and the shift attempts are stopped. To re-attempt the desired shift, the selector switch will need to be rotated to the current position until the switch debounce timer expires then a shift will need to be requested again.

At the end of the 5th blocked attempt, the shift motor is driven towards the last known 'D' channel position. If this motor drive allows the transfer case to reach the 2WD/AWD 'D' channel, or the 2WD/AWD between gear position on the 4H side of 2WD/AWD, the shift is considered complete and the shift attempts are ended.

If the mode sensor is in the NEUTRAL region at the expiration of the shift timer, the TIPM 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 from NEUTRAL, if all 5 attempts fail to reach the desired position (which by default is 4H), the motor will be driven to stall in the direction of 4H or 4L, depending on the achieved position. If the transfer case has reached the 2WD/AWD or 4L between gear position nearest the NEUTRAL positions and the shift conditions are no longer being met, the transfer case will be driven toward the corresponding 'D' channel. Otherwise, the transfer case will be driven in the direction opposite the last attempt with the desired target being 4H or 4L.

If the transfer case reaches the 2WD/AWD 'D' channel when being driven in the 4H direction, then one final 1.0 second drive toward 4H is attempted. If the transfer case then reaches any of the 4H positions, the shift is considered complete and the 4H LED is illuminated. If the transfer case is still the 2WD/AWD position, the shift is considered complete and the 2WD/AWD LED is illuminated.

NOTE: If after the 5th blocked shift and reversal attempt, if the transfer case position is in the NEUTRAL region, shift attempts will continue until a non-NEUTRAL 'D' channel is reached.

SHIFT REVERSAL TARGETS

If the shift timer expires (1 second per 'D' channel) and the transfer case has not reached 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/AWD position, the motor stops at that position. The TIPM 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 position, 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 TIPM should never go to NEUTRAL unless the driver is commanding it and all required conditions are being met

ENCODER DRIFT CORRECTION

Whenever a shift is completed, the TIPM stores the position in memory as the transfer case's intended position. The TIPM continuously monitors the mode sensor and if the mode sensor drifts toward into a NEUTRAL region sensor position for 2.0 seconds, the TIPM will perform a motor drive to correct the drift. The transfer case will be driven toward the intended position for 1.0 seconds ± 100 msec. The TIPM will wait for 2.0 seconds ± 50 msec. and repeat the attempt to shift to the desired position. This will continue until the intended position is reached.

SHIFT MOTOR BRAKING

Two modes of shift motor braking are employed to improve shift performance, static and dynamic. Static shift motor braking is utilized under the following conditions:

- Whenever the transfer case is in the 2WD/AWD or 4L 'D' channel position.
- Whenever an invalid mode sensor code is present.

Static motor braking is achieved by applying +12V on both shift motor wires.

NOTE: Static Shift Motor Braking is independent of ignition key position.

SHIFT ATTEMPT LIMIT

To protect the transfer case system, the TIPM 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 prevent 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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