This TSB affects 2011/12 F250's to F550's built before 2/6/2012

Issue: Some of these vehicles equiped with 4X4 may exhibit a lack of engagement of the 4X4, not staying engaged and/or unlocking in extreme cold temperatures below -18 degrees Celsius or 0 degrees Fahrenheit.

Service proceedure: change front axel jub seals, axel shaft snap rings, front knuckle seals, and replace the module (with or without electronic shift on the fly).

I experienced this issue recently and the dealer performed the work, however the problem has not been rectified. In fact, the temps lately have been just below freezing, and the ESOF won't work properly.

Back to the dealer she goes!

Sam