My 2004 T/B LS 4wd service light came on "just in time for winter". Dealer diagnosed this as some motor that is used in the 4wd system had failed and of course needs to be replaced for $600. The service light comes and goes and if I try the 4All and 4Hi, it kind of bogs down , rumbles and ends with a thud when I shut the 4wd off. More @Wikipedia
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