Pre safe inactive will be displayed after a low voltage or battery disconnect. If there are no faults with the vehicle all that needs to be done is re-synchronize the passenger seat, steering column, windows, sunroof and initialize the steering angle sensor.
Car has 43,000 miles, everything else works fine. Not sure when this message came up but the car is at the dealer right now and will be delivered to my house sometime this week.
What does the message indicate? Does the ECU need a reset?
If Pre-Safe senses a possible accident (very hard braking or braking while swerving usually) it cinches up the seatbelts, moves the seat to the optimal crash position and closes the sunroof -- all in milliseconds. I've managed to trigger the system a couple of times and it works very well. It's quite a thrill to have your seatbelts confirm that your passing maneuver was world-class. They make a kind of Robocop sound as they cinch up and then relax again as soon as they realize all's clear.
One of the sensors or control modules in the system has failed or needs calibration. It could be brake electonics, stability control or a Pre-Safe module. You want it working. It's one of those systems that makes an S-Class an S-Class.