I knew I'd seen this asked recently so did a quick search and found "steviewevie" had provided the following answer ....
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See the vin plate, where it says "axle" there are 4 characters, e.g. A02A or A02B.
Check the fourth character - "A" means open (non-LSD) diff and "B" means LSD.
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You can find the whole thread here ...
http://www.lexusownersclub.co.uk/forum/ind...showtopic=59200
Hope that helps.
TG