When the fuse is removed or the 4WS is faulty, the rear wheels are only held facing forward by springs and as such they can still move when given enough force. In the UK there are reports of cars crabbing due to faulty 4WS. The only way to safely disable the 4WS is to get a 2WS rear fame and do a conversion.
The only time I would ever reccomend do this is if the 4WS is beyond economical repair, I like my 4WS on my 5G too much

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