Quote:
Originally Posted by RocketyMan
Here is the wiring diagram. The actuator gears are plastic...stock. Therefore, I wouldn't be applying voltage at a whim because you can easily strip them--and it's sorta a pain in the butt to replace it because of the heatshield n stuff.
On normal operation, the xcase is only in use under speeds of about 25mph-ish and then in some slip instances. Other than that, it is "off" in normal driving conditions. There is a strategy to help prevent over/under-steer conditions, and I've noticed this myself when going around a sharp corner and hitting the road-"turtles" causing a wheel to slightly slip. Other than that, I wouldn't recommend driving around with the xcase in fully engaged AWD. Also, this will completely wear out the clutches as they will be sacrificed. These xcases are north of $1500 rebuilt.
At usual key-on/off events, the vehicle determines where the end points are on the xcase. I think this is done with calculation of the current draw in correspondence of the actuator.
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Calibration sequence:
When terminal 15 is OFF, a calibration sequence is performed. During this calibration sequence, a certain angle setting of the VTG actuator motor has a corresponding locking torque assigned. The effects of wear are also taken into account when this is done.
The multi-plate clutch is closed fully and separated once during this calibration sequence. When this happens, the current draw is measured at the respective angle setting of the VTG actuator motor. This determines the beginning and end of the closing movement for the multi-plate clutch. The angle setting is recorded by means of the integral incremental sensor in the VTG actuator motor. These values are stored and are used as data when the car restarts.
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Very interesting, thanks! In addition to this E83 X3 3.0, we also have an E53 X5 4.4, with apparently a slightly larger version of basically the same transfer case. I still think it would be cool to lock and unlock at least the X5 on demand, such as for snow-covered roads at highway speeds (especially if I were to use it for wintertime towing to ice races, etc.). I did buy one metal gear to replace a plastic VTG actuator gear, but never installed it in either SAV.
I've determined with a multi-meter that our X3 apparently got stuck in 4wd (TC clutch plates fully engaged) due at least in part to a burned F80 40A fuse for the VTG control unit. It's an odd-looking fuse (pic attached) that looks more like a semiconductor transistor than a fuse. With battery connected, the voltage on the left side of the fuse measured over 12V, and the voltage on the right side a mere fraction of a volt. I've never dealt with a fuse like this before. Is the discoloration towards the bottom right a sign that it blew, or just a coincidence? Is this a dealer-only item?
Now, why that fuse blew is an open question... Although I'd forgotten, one possibility might be because I'd apparently replaced the X3 VTG control unit with a boneyard X5 VTG control unit over a year ago. It worked great this past winter! I thought I'd recoded, but ISTA just reminded me that the VTG control unit in our X3 is still coded as an "X5" unit, FWIW. Another possibility is simply that something shorted as I drove through that deep water on the highway last week. I suppose the actuator and/or connector probably aren't completely waterproof for immersion versus mere splashing.
EDIT: I did some more digging and learned that this particular type of bolt-down fuse is a slow-blow or time-delay "Midi" fuse.