90 Quattro 20V (Canada) L5-2309cc 2.3L DOHC (7A) (1989)
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Control Unit: Description and Operation
Circuit Description
The rear differential lock is operated by a vacuum servo mounted on the rear final drive housing. Engine manifold vacuum to operate the servo is
controlled by the differential lock control unit, which can in turn be activated by the driver-operated differential lock switch on the center console.
The rear differential lock switch, mounted on the rear final drive housing, is activated mechanically when the differential locks. It completes the ground
side of the circuit for the differential lock indicator, illuminating the indicator light on the center console.
The speedometer also provides an input to the differential lock control unit. When the car's speed exceeds 15 mph, the control unit automatically
disengages the differential lock
