Need details of Electronic 4wd selection

[Stref]

I have accessed the wiring diagrams for my 2009 Ram 3500 QC CTD from the Ram Bodybuilder site. I thought that I could figure out what happens when the "Selector Switch" is moved from one position to another, but I can not. From the diagrams I cannot find a connection from the "Selector Switch" to the Transfer Case or TIPM, only to the "Cluster". I would like a detailed explanation of what happens when I make a selection, starting with the output of the "Selector Switch" (ie. what is the output voltage, what is the output name and pin number). I don't care about the mechanics, only the signals to and from the transfer case, using the wiring diagrams nomenclature (ie. TIPM, Sensor Return, Shift Motor Control A, Shift Motor/Mode Sensor Assembly, etc. ). This is a tall request, but I have spent a lot of time searching for this info without success. All I can find is how the system works mechanically.

 

[HBarlow]

The switch probably sends a signal to the ECM/PCM and the control signal comes out. It's very unlikely you'll ever be able to tinker with that function.

 

[Stref]

The switch probably sends a signal to the ECM/PCM and the control signal comes out. It's very unlikely you'll ever be able to tinker with that function.

If this is so, I don't understand why the wiring diagram doesn't show a path to the ECM/PCM.

 

[Bob V]

Its kind of like USB connection. There is data transferred to the PCM, usually a resistance value that lets the computer know the position of the switch.

 

[Stref]

Its kind of like USB connection. There is data transferred to the PCM, usually a resistance value that lets the computer know the position of the switch.

I checked the wiring diagram again and see that the circuit designations (K77 and K977) are for the "Powertrain Control Module", but it does not show a connection to it. Maybe it is one of those boxes in the diagram. I know it isn't a wireless connection. Somewhere there is a missing piece to this puzzle.

 

[PFranzese]

I don't have a diagram in front of me so this is an assumption on my part, I would think the K77 and K977 are the pin positions in the PCM plug. Again this is an assumption since I don't have a diagram.

 

[sag2]

The Readers Digest version.
Selector is a MUX switch (variable resistor) and sends the desired position to the cluster. Cluster uses CAN Bus to tell the TIPM to perform the shift.

From service info (the technical version).
The selector switch assembly is mounted in the left side of the vehicle's Instrument Panel (IP) and consists of a rotary knob connected to a resistive network for the mode and range shift selections. Also located in this assembly is a recessed, normally open momentary switch for making shifts into and out of transfer case NEUTRAL. A pen, or similar instrument, is used to make a NEUTRAL shift selection, thus reducing the likelihood of an inadvertent shift request.

The selector switch also contains four light emitting diode's (LED's) to indicate the transfer case position and whether a shift is in progress.

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
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.
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)
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)
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.

As the position of the selector switch varies, the resistance between the Mode Sensor supply voltage pin and the Mode Sensor output will vary. Hardware, software, and calibrations within the Transfer Case Control Module (TCCM) are provided that interpret the selector switch resistance as given in the table below: SELECTOR SWITCH INTERPRETATION



SELECTOR SWITCH INTERPRETATION
Step Resistance Range (ohms) Required Interpretation
A <200 Shorted
B 400-700 NEUTRAL
C 1050-1450 4LO
D 1850-2300 4HI
E 3050-5950 2WD (Default)
F 9. 5-12. 5K In between positions
G >15. 5K Open

For resistances between the ranges B-E shown for each valid position (T-Case NEUTRAL, 4LO, 4HI, 2WD), the TCCM may interpret the resistance as:

either of the neighboring valid positions.
as an invalid fault position.
For resistances between the ranges E and F shown for 2WD and in-between positions, the TCCM may interpret the resistance as:

the 2WD position.
an invalid fault position.
a valid in-between position.
For resistances between the ranges F and G shown for in-between positions and fault condition (open), the TCCM may interpret the resistance as:

a valid in-between position.
an invalid fault position.
For resistances between the ranges A and B shown for the fault condition (short) and T-Case NEUTRAL, the TCCM may interpret the resistance as:

the T-Case NEUTRAL position.
an invalid fault position.
The LED's in the selector assembly are illuminated/flashed in the following manner to indicate a particular condition or state.

A solidly illuminated LED indicates a successfully completed shift and the current operating mode of the transfer case. While a shift has been requested but not yet completed, the LED for the desired transfer case position is flashed.
A flashing operating mode LED for the desired gear indicates that a shift to that position has been requested, but all of the driver controllable conditions have not been met. This is in an attempt to notify the driver that the transmission needs to be put into NEUTRAL, the vehicle speed is too great, or some other condition outlined (other than a diagnostic failure that would prevent this shift) elsewhere (Refer to 08 - Electrical/8E - Electronic Control Modules/MODULE, Transfer Case Control - Operation) is not met. Note that this flashing will continue indefinitely until the conditions are eventually met, or the selector switch position is changed, or if diagnostic routines no longer allow the requested shift.
If the driver attempts to make a shift into transfer case NEUTRAL, and any of the driver controllable conditions are not met, the request will be ignored until all of the conditions are met or until the NEUTRAL select button is released. Additionally the neutral lamp will flash, or begin to flash while the button is depressed and operator controllable conditions are not being met. All of the LED's except the Neutral will flash if any of the operator controllable conditions for shifting are not met while the Neutral button is depressed. This "toggle" type of feature is necessary because the TCCM would interpret another request immediately after the shift into transfer case NEUTRAL has completed.

 

[Stref]

Sag2, Thank yor for that excellent detail of the 4WD operation.

 

[Bob4x4]

Sag2, Thank yor for that excellent detail of the 4WD operation.

Now don't mess it up... ... ... ... ... ... ... . all the parts are pricey

 

[Stref]

It appears that the problem has been found by Planet Chrysler Jeep in Flagstaff, AZ. The 5 volt supply to the T-case Shift Motor was intermittent due to a defective female pin in C130. The spring tab inside the female pin that pinches the male pin was bent flat. If anyone can tell me how interruption of this 5 volts supply will cause the system to want to go into "4LO" from "2WD" I would appretiate it.