I was playing with Ideas and have found a possible solution for uncommand shifts
If we look at the motor (pins 4 & 5) and follow the (relaxed) state logic you will note
1. Both wires are connected together
2. They both are running to chassis ground
The (Motor Brake) is not provided from the ground, it's provided from both sides of the motor being tied together
So, one could install a (DPDT) switch in this circuit and have it wired so
1. Position 1 - normal operation
2. Position 2 - Tow Mode
In tow mode position -
- You create an open circuit from the BJB on both motor feed wires at the switch
-You create a jumper connection between both sides of the motor
- For circuit protection (in the event) of a switch failure, do not add a chassis ground
The reasoning for not adding a ground here is simply to protect the circuit (if a switch failure occurred) you would have a short to ground and blow the 4WD Relay fuse with an added ground
So, the procedure would be - after you are all done and (Neutral Tow) is set and truck is shut off, flip this switch. - VERY LAST STEP
and the opposite for disable - make it the VERY FIRST STEP
The only drawback is - if the truck tries to power the motor it's going to generate a - 4x4 fault
but you have taken away any chance of the motor - moving with the by-pass switch in tow position.
I want to also highlight something here that I am noting and it has to do with the (Braking) effect on the circuit.
The circuit must see a (Series Loop) on both sides of the motor, thinking outside the box here and wondering (What If?) either relay contact (at rest) was pitted this would create and high resistance in the circuit - therefore creating an open, now we have lost that braking effect and road vibrations etc could possibly let the shift motor move, not from any electrical command just simply a bad circuit completion
So, to summarize - my switch by-pass idea - also addresses this possible scenario and this just might be the smoking gun for some of the uncommented shift reports.
The VREF Feedback:
The VREF - circuit remains happy as it can still ref (commanded) position (Neutral)
So, in a (Brownout) event and the (modules) drop neutral tow memory the PCM will attempt to command the shift - but will be electrically blocked from the open circuit, so worst case scenario it will generate faults, but the motor will not be able to engage and damage the transmission
So yes, you would have to cut and splice into the wire harness, but this is the simplest way (Quick and Easy) for transitions in and out of (Neutral Tow)
Now the Transmission (Neutral or Park) Debate
I look at it this way -
With the T-Case in (Neutral) and Transmission in (Neutral) the T-Case is physically disconnected from the transmission - yes there may be some resistance spinning inside the transmission as it makes sense, but it would be minimal
In the failure event - the T-Case shifts out of (Neutral Tow) and the transmission begins actually dry spinning and overheating the transmission (no fluid movement) for cooling
If the transmission is in (Park) during this failure event - the park pawl would instantly shear off, and you would have the same dry spinning and overheat event.
Debate: Fence
In (Neutral) you have some slim chance of the transmission not being damaged and it depends on how long the drive was with the T-Case was engaged -50% Chance
In (Park) you have immediate confirmed damage - starting with the park pawl and possible cracked transmission case - 100% Chance
Which one would you prefer to (Risk)
There is so much SW logic that is unseen, and that makes any attempt to circumvent / modify much more difficult. Unseen consequences are to be expected.
