Is the 1991 Ford Aerostar electronic all wheel drive on all the time or only active in slipping conditions?

all wheel drive is active all of the time I have not heard of the all wheel drive , I have the 94 electronic 4 wheel drive , it is only active in loss off traction !! Good Luck ! The electronic 4wheel drive is automatic. When there is little to no load on the engine when it is in gear, it triggers an electric sensor switch (hence the name "electric four wheel drive") that engages the rear wheels. You will know when it's working. It will only tell you if four wheel drive has a problem, not whether or not it is on. You will feel it kick and then you start moving. I drove through an underpass that was in about 1' deep water, and as soon as i pushed the pedal and the front wheels slipped, it kinda jerked and the rear wheels started spinning as well. I hope that answers your question. Matt Hecker of Springfield Oregon I have an electronic 4WD Aerostar..a 1997. I understand that the 4WD it is active all the time with a 30% front and 70% rear power delivery to the wheels under dry-road conditions. When there is a loss of traction (e.g. if you're suddenly on a patch of ice), and the wheels skid, the power distribution becomes 50% rear, 50% front. On mine, there is an alarming jerk in the transmission, like you've gone over a railroad track. I'm not sure whether this is normal or not. However, at low speeds the aerostar is terrific in snow...I've driven though a snow covered ploughed field with it...it's awesome.