Airbag - Testing Emergency Tensioning Retractor & Airbag
TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERSDATE: July 1986 REF. NO. 91/34
SUBJECT: A. TESTING EMERGENCY TENSIONING RETRACTOR (ETR)
B. TESTING AIRBAG WITH ETR
A. Testing ETR
The electrical test indicates whether the ignition circuit and individual squibs of the ETR's are operational (Part 1, steps 1-4). If the required resistance values are not obtained, individual tests can be performed, and action may be taken to rectify any problems.
During the functional testing (Part II) of the mechanical components, the ETR removed from the vehicle can be physically checked to determine if it has been actuated.
B. Testing Airbag with ETR
Since Model Year 1984, squibs with resistance values of 2.15 +/- 0.35 ohms (previously 4.5 +/- 0.5 ohms) have been installed in production, thereby changing test step 4, Testing the Airbag with ETR, in accordance with job no. 91.7-700 (see Modified Repair Instructions, job no. 91.7-700, page 7).
NOTE: The above mentioned resistance value is of the squib only and does not include any wiring harness resistance.
Figure 1 - Wiring Diagram ETR Model 201 (see ETM for Other Models):
A. Testing ETR
I Testing the Ignition Circuit and Squibs
1. Disconnect and cover the negative battery terminal.
Figure 2 - Model 107 4-Pole Test Plug At Parking Brake:
Figure 3 - Model 123 4-Pole Test Plug Under Driver Seat:
Figure 4 - Models 124, 126, 201 Under Front Passenger Footrest:
2. Connect the Ohmmeter to the 2 connected terminals of the 4 pole test Coupling (use Electrical Connection Kit 201 589 00 99 00).
NOTE: The test connection X29 is connected in parallel with the squibs of the ETRs.
N2/1 ETR control unit
R12/1 Left front ETR squib
R12/2 Right front ETR squib
W1
Main ground (behind instrument
Cluster)
X28/1 Connector, ETR voltage supply
X29 Test Connection, ETR
a To fuse box input terminal 15R
3. Measure the leakage resistance from the test connection against ground.
Resistance value: 20k ohms or greater.
If the resistance value is not obtained replace the wiring harness set.
Figure 5 - Measure Circuit Resistance:
4. Measure circuit resistance (Figure 5).
Resistance value: 1.2-1.7 ohms.
If the resistance value is obtained then End of Test.
If the resistance value is not obtained, continue with test.
Figure 6 - Disconnect Electrical Connector from Right ETR and Measure Resistance:
Individual Test of the Squib and Wiring Harness
5. Test the left ETR squib and wiring harness.
Gain access to the right ETR, disconnect the electrical connector from the ETR (Figure 6), and measure the resistance at the 4-pole test plug.
The resistance should be approximately double that of the value obtained in test step 4.
Resistance value: Approx. 2.5 ohms.
If the resistance value is OK, continue with test step 6.
If the resistance value is not OK, test the wiring harness for an open circuit.
Figure 7 - Bridge Plug Terminals:
Gain access to the left ETR, disconnect the electrical connector from the ETR and bridge the two plug terminals (Figure 7).
Measure the resistance on the 4-pole test plug.
Resistance value: less than 1 ohm
If the resistance value is OK, replace the left ETR unit.
If the resistance value is not OK, replace the wiring harness.
6. Test the right ETR squib and wiring harness.
Gain access to the left ETR, disconnect the electrical connector from the ETR, and measure the resistance at the 4-pole test plug.
The resistance should be approximately double that of the value obtained in test step 4.
Resistance value: Approx. 2.5 ohms.
If the resistance value is not OK, test the wiring harness for an open circuit.
Gain access to the right ETR, disconnect the electrical connector from the ETR and bridge the two plug terminal.
Measure the resistance at the 4-pole test plug.
Resistance value: less than 1 ohm.
If the resistance value is OK, replace the right ETR unit.
If the resistance value is not OK, replace the wiring harness.
NOTE: In a badly damaged automobile, the sensor on the transmission tunnel must be checked for a visibly deformed or damaged housing. If the sensor housing is deformed or damaged it must be replaced.
Test Equipment
Name Designation
Digital multimeter SUN-DMM5
Special Tools
Name Part Number
Electrical connection 201 589 00 99 00 kit
Time Allowance
Test Step 1-4:
91-0858/00 Emergency Tension Retractor Ignition Circuit, Test 0.3 hrs.
(with Repair Work)
Test Step 5 & 6:
91-0859 Squib with Wiring Harness - Both Sides, Test (after Ignition Circuit Test)
/53/55/73 2.1 hrs.
/11/15 0.7 hrs.
/80/40/51/52/54/56/57/71/72 0.5 hrs.
Figure 8 - Check for Visibility of Green or Yellow Color Marking on Cable:
II Functional Test of Mechanical Components (ETR removed and electrically disconnected)
1. Check if the color marking (green or yellow) is still visible on the cable (arrow, Figure 8).
If the color marking is still visible then the ETR was not actuated.
If the color marking is not visible then the ETR was actuated.
Figure 9 - ETR Unit:
2. During production phase-in, a few vehicles were manufactured without the color marking on the cable. These should be tested as follows:
Remove protective rubber cap on tube end and measure length "X" (Figure 9) by inserting a small diameter (approximately 10 mm) round object, such as a screwdriver, into the tube and measuring the inserted length.
CAUTION! Be sure that the ETR is disconnected when inserting any object into the tube.
Model Length "X"
107 140 mm +/- 5 mm
123 140 mm +/- 5 mm
124 170 mm +/- 5 mm
126 170 mm +/- 5 mm
201 170 mm +/- 5 mm
If length "X" is shorter than the respective length in above table, then the ETR was actuated and must be replaced.
Modified Repair Instructions:
Modified Repair Instructions:
B. Testing Airbag with ETR
Modified repair instructions job no. 91.7- 700 (test step 4).
NOTE:
Since Model Year 1984, squibs with resistance values of 2.15 +/- 0.35 ohms (previously 4.5 +/- 0.5 ohms) have been installed in production, thereby changing test step 4, Testing the Airbag with ETR, in accordance with job no. 91.7-700.
Wiring Diagram of Airbag and ETR, Model 126 up to M.Y. 1985 (see ETM for Other Models):
Ale15 SRS indicator W1 Main Ground (behind instrument
C1 SRS energy accumulator cluster)
N2/2 SRS control unit X28/2 Connector, SRS voltage supply
N24 SRS voltage convertor X28/4 Connector, air bag squib (2 pole)
R12/1 Left front ETR squib X28/5 Connector, air bag squib slip ring
R12/2 Right front ETR squib (2-pole)
R12/3 Airbag squib a to input side of fuse no. 9, circuit
15R