ETR Control Module with Airbag, General Information

The airbag and ETR restraint system has a control module with integrated energy accumulator and voltage converter.

The task of the ETR with airbag control module, also known as the activation unit or crash sensor, is to calculate the severity of the collision in the event of an accident and to activate the restraint system in good time, if necessary.

Control module version (up to approx. 06/93 and USA)

12 Pin:

16 Pin:

Operating principle

The control module processes the deceleration of the car during a head-on collision and is rigidly connected on a bracket to the transmission tunnel of the car. As a result of an integral safety switch which interrupts the ignition circuits of the driver airbag and ETR restraint system, airbag and emergency tensioning retractor can only be ignited if a deceleration actually exists. This eliminates the risk of malfunctions.

An acceleration sensor integrated in the control module detects the deceleration to which the car is subjected in the longitudinal direction and passes a signal, which is appropriately conditioned, to the threshold switch, for analysis. If the set triggering thresholds of the two thresholds switches are exceeded, the output stages are switched through in accordance with the states detected at the seat belt buckle switches (latch inserted in buckle or not). This causes the restraint system to be triggered. If the power supply is interrupted during an accident, the driver airbag can still be ignited within 100 ms but not the two emergency tensioning retractors. The SRS malfunction indicator lamp (A1e15) comes on if the system voltage is < 9.5 V for longer than 10 s, and goes out if the voltage is > 10 V.

The housing and electrical connections are designed so as to reliably eliminate the possibility of any malfunctions resulting from electrical interference in the car's electrical system caused by connecting electrical components and by electromagnetic, radiated interference on public roads.

NOTE: The control module must be replaced after an accident in which the airbag was activated.

The fault memory of the control module can be read only with the pulse counter.

New buckles with separate switches and resistors are required to properly detect whether the latches are inserted in the buckles or not. This then produces the activation logic presented below.





S68/3 Left front seat belt buckle/airbag (AB) ernergency tensioning retractor (ETR) switch

S68/4 Right front seat belt buckle/airbag (AB) emergency tensioning retractor (ETR) switch

Activation Logic (up to Approx. 06/93) - Driver Airbag:

Explanatory notes:
If the severity of the accident is only slight and the protection offered by the driver seat belt is adequate, only the emergency tensioning retractor is activated if the 1st threshold is exceeded, provided the belt latch is inserted in the buckle.

If the latch of the driver seat belt is not inserted in the buckle, the driver airbag is activated as a protection for the driver.

If the 2nd activation threshold is exceeded and the belt latch is inserted in the buckle, the driver airbag is additionally activated.

Activation Logic (up to Approx. 06/93) - Driver & Passenger Airbag:

Explanatory notes
If the severity of the accident is only slight and the protection offered by the seat belts is adequate, only the emergency tensioning retractors are activated if the 1st activation threshold is exceeded, provided the belt latches are inserted in the buckles.

If the 1st activation threshold is exceeded and the belt latches are not inserted in the buckles, the two airbags are activated as a protection for the driver and passenger.

If the 2nd activation threshold is exceeded and the belt latches are inserted in the buckles, the driver and passenger airbags are activated.

Block Diagram - Overall Function (up to 06/93):