Seat Belt Tensioner: Testing and Inspection

Belt Tensioner Testing on Vehicles WITHOUT Airbag: For vehicles with Airbag, [1][2]Component Tests and General Diagnostics

Special Tool:

Testers:
Digital pocket multimeter e.g. Hermann Avometer 2003
e.g. Fluke, 23
Multimeter e.g. Sun, DMM-5

The following tests for triggering or function must be performed:
a) Following an accident with visible deformation to:
- the guide rail.
- the belt retractor.
- the belt buckle.
b) After removing a belt tensioner.
c) After installing optional equipment requested by the customer, which may influence the function of the belt tensioner system either mechanically or electrically.

This test program is divided into:
A. Mechanical function
B. Electrical function

A. Mechanical Function:





Testing the belt tensioners for triggering (center pillar covering or belt tensioner removed).

Cable Tensioner (1st version, 2nd version), Check whether the colored mark on the cable (green or yellow) is still visible. If the colored mark is still visible, the belt tensioner has not been triggered. If no colored mark can be seen, the belt tensioner has been triggered and must be renewed.





When the series was introduced, some vehicles were built with no colored mark on the cable of the belt tensioner. These must be tested as follows:
- Remove protective rubber cap on end of tube and measure distance "X". To do this, insert a round implement or screwdriver of approx. 10 mm diameter and measure the depth.

Model Distance "X"
201 170 mm ± 5 mm

If the measured distance is shorter than the distance given above, the belt tensioner has been triggered and must be renewed.





As of 01/86, there is an observation window in the housing of the belt tensioner, through which the cable is visible. This means that it is no longer necessary to remove the belt tensioner for the test. Belt tensioners where no cable is visible have been triggered and must be renewed.

As of 08/87 belt tensioners are supplied by two manufacturers.





There is also an observation window on the housing of Autoflug belt tensioners, through which 2 cables are visible. Autoflug belt tensioners where only 1 cable or no cable is visible, have been triggered and must be renewed.

Autoflug belt tensioners have always been equipped with an approx. 80 mm shorter tube than the Repa belt tensioners. Repa belt tensioners also incorporate this shorter version of tube as of 01/88.

B. Electrical Function:

Belt Tensioner Wiring Diagram:

N2/1 Control unit, belt tensioner
R12/1 Detonator, belt tensioner, front left
R12/2 Detonator. belt tensioner, front right
X28/1 Plug connection, power supply, belt tensioner
X29 Test coupling, belt tensioner
W12 Main ground point, center console
a To fuse box, terminal 15 R

Testing the Triggering Circuit of the Detonators:
1. Disconnect negative terminal of battery and cover.
2. Connect multimeter to the 4-pin test coupling (X29) (2 pins used).

NOTE: The test coupling (X29) is connected in parallel with the detonators.

Location of 10-Pin Plug Connection or the 4-Pin Belt Tensioner Test Coupling in the Vehicle:

1st version - Under footrest in passenger's footwell:

2nd Version - On plate under footrest in passenger's footwell:

Testing:

















NOTE: If the vehicle is severely damaged, the control unit (N2/1) on the transmission tunnel must be checked for visible deformation or damage to the housing. Control units with damaged housings must be renewed.