Four Wheel Drive Selector Switch: Description and Operation
SELECTOR SWITCHDESCRIPTION
The selector switch assembly (Fig. 95) 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
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
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 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.
^ No LED's illuminated indicate a fault in the transfer case control system.