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B2442, B2447

B2442, B2447

Seat belt tensioner, driver / Seat belt tensioner, passenger, short circuit to ground

The reference resistor is available in two versions. A newer, part no. 86 12 095 , and an older, part no. 84 71 153 . The new type has closer tolerance limits and should be used for more reliable diagnosis. The illustrations in the following chapter show the older type of reference resistor.
















Diagnostic procedure


1. Connect the diagnostic tool. Note the diagnostic trouble code and type of fault.


P=permanent fault, I=intermittent fault.

If the fault is permanent:

Go to point 3.

If the fault is intermittent:

Go to point 2.

2. The fault is intermittent. Try to provoke the fault at each test section in the continued fault diagnosis.

Move the connectors and cables and turn the steering wheel while testing.

Go to point 3.

3. Turn off the ignition and remove the negative cable from the battery. Undo the bolts securing the steering wheel airbag. Unplug the connector from the back of the airbag and connect the reference resistor 84 71 153 to the connector.


On cars with airbag on passenger side;

3.a. Remove the glove-box and unplug the connector on the back of the passenger airbag.

3.b. Connect the reference resistor 84 71 153 to the connector.

Remove the trim on the B-pillars. Unplug the connectors to the seat belt tensioners. Connect reference resistor 84 71 153 to the connector.

Go to point 4.

4. Refit the negative cable to the battery and turn on the ignition. Clear the fault codes. Turn off the ignition and turn it on again, wait for at least 10 seconds with the ignition on.


Check to see if the diagnostic trouble code returns.

If the diagnostic trouble code returns:

Go to point 7.

If the diagnostic trouble code does not return:

The fault is in the driver or passenger seat belt tensioner. Perform an extra check as described in point 5.

5. Turn off the ignition and remove the negative battery cable. Remove the reference resistor from the seat belt tensioner connector on the driver's side and connect the seat belt tensioner.


Refit the negative cable on the battery and turn on the ignition. Wait for at least 10 seconds with the ignition on.

Check to see if the diagnostic trouble code returns.

If the diagnostic trouble code returns:

Turn off the ignition. Remove the negative battery cable and change the seat belt tensioner. Then go to point 13.

If the diagnostic trouble code does not return:

The fault is in the seat belt tensioner on the passenger side. Perform an extra check as described in point 6.

6. Turn off the ignition and remove the negative battery cable. Reconnect the reference resistor on the seat belt tensioner connector on the driver's side.


Remove the reference resistor form the seat belt connector on the passenger side and connect the seat belt tensioner.

Refit the negative cable on the battery and turn on the ignition. Wait for at least 10 seconds with the ignition on.

Check to see if the diagnostic trouble code returns.

If the diagnostic trouble code returns:

Turn off the ignition, remove the negative battery cable and change the passenger seat belt tensioner. Then go to point 13.

If the diagnostic trouble code does not return:

Turn off the ignition and remove the negative battery cable. Unplug the connector from the seat belt tensioner and then go to point 7.

7. Turn off the ignition and remove the reference resistor from the two seat belt tensioner connectors. Expose the SRS control module. Unplug the SRS control module connector and connect a BOB to the wiring harness.


Test of driver's side seat belt tensioner:

Connect an ohmmeter between connector 1 on BOB and a good grounding point. Then connect the ohmmeter between connection 2 on BOB and a good grounding point. In both cases, the ohmmeter should read infinite resistance.

If the value is OK:

Go to point 10.

If the value differs:

Go to point 8.

8. Unplug the 4-pin connector on the floor tunnel under the carpet, approx. 20 cm in front of the SRS control module.


Measure the resistance in the wiring harness between the SRS control module and the 4-pin connector:

Left-hand drive cars (LHD):

Connect an ohmmeter between sleeve 1 in the connector female and a good ground. Then connect the ohmmeter between sleeve 2 in the connector female and a good grounding point.

Right-hand drive cars (RHD):

Connect an ohmmeter between sleeve 3 in the connector female and a good ground. Then connect the ohmmeter between sleeve 4 in the connector female and a good grounding point.

In both cases, the ohmmeter should indicate infinite resistance.

If the value is OK:

Go to point 9.

If the value differs:

If any of the readings indicates a low resistance, there is an overload to ground in the wiring harness between the 4-pin connector and the SRS control module connector. Locate the cause and change the wiring harness.

Then go to point 13.

9. Measure the resistance in the wiring harness between the seat belt tensioner and the 4-pin connector:


Left-hand drive cars (LHD):

Connect an ohmmeter between pin 1 in the connector male and a good grounding point. Then connect an ohmmeter between pin 2 in the connector male and a good grounding point.

Right-hand drive cars (RHD):

Connect an ohmmeter between pin 3 in the connector male and a good grounding point. Then connect an ohmmeter between pin 4 in the connector male and a good grounding point.

In both cases, the ohmmeter should indicate infinite resistance.

If the value is OK:

Go to point 13.

If the value differs:

If any of the readings indicates a low resistance, there is an overload to ground in the corresponding lead between the seat belt tensioner connector and the 4-pin connector. Locate the cause and change the wiring harness.

Then go to point 13.

10. Test of passenger side seat belt tensioner:


Connect the ohmmeter between connector 3 on BOB and a good grounding point. Then connect the ohmmeter between connection 4 on BOB and a good grounding point. In both cases, the ohmmeter should indicate infinite resistance.

If the value is OK:

Go to point 13.

If the value differs:

Go to point 11.

11. Unplug the 4-pin connector on the floor tunnel under the carpet, approx. 20 cm in front of the SRS control module.


Measure the resistance in the wiring harness between the SRS control module and the 4-pin connector:

Left-hand drive cars (LHD):

Connect an ohmmeter between sleeve 3 in the connector female and a good ground. Then connect the ohmmeter between sleeve 4 in the connector female and a good grounding point.

Right-hand drive cars (RHD):

Connect an ohmmeter between sleeve 1 in the connector female and a good ground. Then connect the ohmmeter between sleeve 2 in the connector female and a good grounding point.

In both cases, the ohmmeter should indicate infinite resistance.

If the value is OK:

Go to point 12.

If the value differs:

If any of the readings indicates a low resistance, there is an overload to ground in the wiring harness between the 4-pin connector and the SRS control module connector. Locate the cause and rectify the fault.

Then go to point 13.

12. Measure the resistance in the wiring harness between the 4-pin connector and the seat belt tensioner on the passenger side:


Left-hand drive cars (LHD):

Connect an ohmmeter between pin 3 in the connector male and a good grounding point. Then connect an ohmmeter between pin 4 in the connector male and a good grounding point.

Right-hand drive cars (RHD):

Connect an ohmmeter between pin 1 in the connector male and a good grounding point. Then connect an ohmmeter between pin 2 in the connector male and a good grounding point.


In both cases, the ohmmeter should indicate infinite resistance.

If the value is OK:

Go to point 13.

If the value differs:

If any of the readings indicates a low resistance, there is an overload to ground in the corresponding lead between the seat belt tensioner connector and the 4-pin connector. Locate the cause and change the wiring harness.

Then go to point 13.

13. Turn off the ignition and remove the negative cable on the battery. Remove the reference resistor and plug in all the connectors to their original components. Reconnect the negative cable on the battery and turn on the ignition.


Clear the fault code. Turn off the ignition and turn it on again. Wait for 10 seconds with the ignition on.

Check to see if the diagnostic trouble code returns.

If the diagnostic trouble code returns:

Go to section: Procedure for replacing the control module .

If the diagnostic trouble code does not return:

Restore the car.