2003 4runner transfer case gears crushed - engine check?

[jackalexander]

My engine check light came on recently. When it did, the TRAC services failed and their lights went on too. My Mech. diagnosed the O2 sensor failed, so we ordered one and I drove away (engine and TRAC lights still on). The next day it snowed, I selected 4wheel drive and immediately noticed a grinding sound. Experimented a little, turned it off.
I had the O2 sensor fixed and asked him to check the grinding. It was the transfer case. Fluids where fine, no leaks. Took it apart and found crushed gears and mangled mounting cage. Also the pump was damaged.

So how does that happen? Could it be that I caused it when switching to 4wheel driver with the enginer and TRAC service light on?

 

[TOY2G]

on our trucks, when you switch to 4wd it will give you a beep if it is not locked in when you try to place it into gear. problem here is that the beep will go out before the tranfercase has fully engaged the 4wd. you will start to drive and the gears will be forced onto each other causing major deflecting. this will normally happen if the 4wd is not used for months at a time.