The official notice
Defect
Over time, the nuts that attach the axle shafts to the axle housing could loosen and fall off. If this happens, one or both axle shafts could separate from the axle housing. This could cause noise and vibration and/or a differential oil leak. An axle shaft that separates can cause reduced braking and vehicle stability.
Safety Risk
Reduced vehicle stability could cause a loss of control. Reduced braking can cause extended stopping distances. Both of these issues could increase the risk of a crash.
Remedy
Toyota will notify owners by mail and instruct you to take your truck to a dealership to inspect the rear axle assembly and retighten the axle flange nuts. For vehicles where other axle-related components are damaged, they will be replaced, if necessary.