Emergency TENSIONING Retractor (ETR)

WARNING: This page is about a different car, the 1993 Mercedes-Benz 500SEL and 1993 Mercedes-Benz 500E. However, it is still accessible from the selected car via links, so may be relevant.

The ETR seat belt assembly consists of a gas generator, cable pulley, clutch, guide tube, automatic seat belt retractor reel, and piston with cable. The complete unit is installed in the right door "B" pillar, in place of standard belt reel unit. The ETR unit is electrically connected to SRS system by a double pin connector.

When ETR unit wiring connector is disconnected, unit is automatically shorted by a safety shorting spring inside connector. This prevents accidental operation of ETR system by static electricity or careless handling. Safety shorting spring contact is automatically disconnected when SRS connectors are reconnected.

The moment an electrical impulse is transmitted from SRS control unit to ETR gas generator to ignite a solid propellant, a quantity of non-toxic nitrogen gas is produced. The gas accelerates piston and cable in upward direction in tube. The cable transmits a turning torque to pulley, causing a shear pin to break off, which connects pulley to wind-up shaft. The wind-up shaft is turned back to eliminate any slack. This action pulls the seat belt snugly against front occupant in milliseconds.