Originally Posted by Subaru STI Type-RA Manual

DRIVER'S CONTROL CENTER DIFF
(SKETCH5046)
(SKETCH5852)
The intent of this mechanism is to adjust the diff lock ratio of the LSD (limited slip differential) as necessary.
Adjusting the dial to "diff free" (indicator: green, empty square, empty triangle) under normal driving conditions, and "diff lock" (bright orange solid triangle) on gravel, snow, in the rain, is effective (probably means suggested). By setting the diff lock ratio as necessary, depending on the various roads and running conditions, unrivaled driving mobility will be demonstrated.

WARNING!
This is not an all purpose vehicle. DO NOT overestimate its abilities. Please use appropriate discretion and drive at safe speeds where there are sudden braking, sudden turns, sudden curbs, snowy roads, slippery roads, etc.

USING THE CONTROL DIAL
(SKETCH5048)
The dial is located next to the handbrake lever, rotating it fully forward is diff free, rotating it fully backward is diff lock. You can continuously change the diff lock ratio using the settings in between.
DIFF FREE: No front and rear LSD (Front to rear power distribution=36:64)
DIFF LOCK: The front and rear have an almost direct connection. (Front to rear power distribution=front/rear load distribution)
(CHART1)

INDICATOR (ON THE METER DISPLAY)
The diff lock ratio is displayed at one of six settings, as it is linked to the control dial. The upper lighted block (orange solid triangle) indicates a greater direct connection.
The true lock ratio can be continuously changed.

ADVICE
• The indicator is the criterion.
• Regardless of what the dial settings are, LOCK will illuminate for one second after the key is turned to the on position.
• At night, while your driving lights are on, the display may appear to go dark for a moment, but this is normal.


CANCELLATION OF DIFFLOCK
Even if the DCCD is set to LOCK (orange), by pulling the hand brake lever, it will automatically go to DIFF FREE, moving all power to the rear wheels. (linked to the brake warning light) However, the indicator will not change.
Once you release the hand brake lever, the DCCD will return to its proper setting.

TIGHT CORNER BRAKING PHENOMENON (makes more sense once you read the following)
When the indicator is orange while driving on dry tarmac/asphalt, corners, and even reverse parking, due to the rotational difference between the front and rear wheels, there are cases where heavy vibration and noise may occur during braking.
Though this is not out of the ordinary, and to resolve this "problem", you can simply either set the DCCD to DIFF FREE or pull the hand brake enough so that the brake warning light illuminates.
While you may feel a light "shock" when using the control dial during quick acceleration and tight cornering, due to the movement of the center diff, this is normal.

WARNING!
• DO NOT use the DCCD while any of the wheels are in mid air.
• Set the DCCD to DIFF FREE while the car is stopped.
• Set the DCCD to DIFF FREE while the car is being pulled or towed. The car can only be towed/pulled either by rope or on a rollback. DO NOT pull or tow the car on only its front or rear wheels. Please see page 195 for more information on warnings related to towing.
• ALWAYS set the DCCD to DIFF FREE when using the emergency spare tire. Change or fix the tire as soon as possible.
• When the center diff requires repair (control unit, disconnected wires, shorted wires, voltage issues, etc.) the DCCD reverts back to DIFF FREE and the indicator (at which you last had it set) should flash at 1 second intervals. Please go to your nearest Subaru dealer immediately. Once a problem arises, even if the unit regains power, it will not reset itself until the engine key is set to the off position.