Actually, (pardon my correction Ottobun), but the 4matic system is always engaged from a stop to about ten miles per hour. It is designed this way. If no wheel slippage is detected, the sytem automatically disengages. If you do a search here on "4matic", about a year ago there was a posting with a link to a very thorough explaiation of the system which is very helpful in understanding not only how it works, but why it works so well. Second, though Ottobun disengages his 4matic with no adverse affects, it is my understanding that when you do this, it also disengages the self leveling suspension pump, which will affect the vehicle's handling. However, as he said, unless the leak is major, you can drive for many miles before a TC replacement is required.