Mercedes-Benz E 300 Operator's Manual page 54

Supplemental Restraint System (SRS)
The term Supplemental Restraint System
means that airbags are intended as a
supplement to seat belts. Airbags alone
cannot protect as well as airbags plus seat
belts in impacts for which the airbags
were designed to operate, and do not
afford any protection whatsoever in
crashes for which the system is not
designed to deploy.
The SRS uses two crash severity levels
(thresholds) to activate either the ETR or
airbag or both. Activation depends on the
direction and severity of the impact,
exceeding the thresholds and fastening of
the seat belt.
Seat belt fastened
• first threshold exceeded: ETR activates
• second threshold exceeded: airbag
also activates
Seat belt not fastened
• first threshold exceeded: airbag
activates, but not ETR
Driver and front passenger systems
operate independently from each other.
Emergency Tensioning
Retractor (ETR)
The seat belts for the front seats are
equipped with emergency tensioning
retractors. These tensioning retractors
are located in each belt's inertia reel
and become operationally ready with
the electronic key in steering lock
position 1 or 2.
The emergency tensioning retractors
are designed to activate only when the
seat belts are fastened during frontal
impacts exceeding the first threshold of
the SRS and in rear impacts exceeding
a preset security level. They remove
slack from the belts in such a way that
the seat belts fit more snugly against
the body restricting its forward
movement as much as possible.
In cases of other frontal impacts,
angled impacts, roll-overs, certain side
impacts, or other accidents without
sufficient frontal or rear impact forces,
the emergency tensioning retractors
will not be activated. The driver and
passengers will then be protected by
the fastened seat belts and inertia reel
in the usual manner.
For seat belt and emergency tensioning
retractor safety guidelines see Safety
Guidelines in Index.
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