B2872

Side Impact Sensor, Driver





Fault symptoms
Airbag warning lamp on.

Conditions
The following conditions are applicable to the respective diagnostic trouble codes:

B2871
- No communication between side impact sensor and control module

B2872
- The voltage on the side impact sensor's communications lead is lower than 3 V for 1.25 s.

B2873
- The voltage on the side impact sensor's ground lead is higher than 6 V for 1.25 s.

Diagnostic help
Diagnostic trouble code B2871 will be generated if the side impact sensor is defective or if the sensor's communications lead (pin 1 on the side impact sensor, pin 41 on the control module) is short-circuited to battery positive (B+) or open-circuit (broken).

Action

1. Check the wiring harness between the control module and the driver's side impact sensor




- Turn the ignition switch to the OFF position.




- Undo the connector: Impact sensor, driver's door: (328D)
- Check and if necessary rectify pins 1 and 2 with respect to open circuit/pin slide-out.




- Undo the connector: Control Module Airbag: (331)
- Check and if necessary rectify pins 41 and 42 with respect to open circuit/pin slide-out.
- Connect a break-out box (BOB) to the mains.
- Take a resistance reading




- Red feed cable: Control module Airbag: 42




- Black feed cable: Impact sensor, driver's door: 2
- The value should be 0 - 2 ohms

Test results OK?

YES
- Go to step 2.
NO
- Repair or replace the wiring.
- Go to step 5.

2. Check the wiring harness between the control module and the driver's side impact sensor
- Take a resistance reading




- Red feed cable: Control module Airbag: 42




- Black test lead: Car battery: B-.
- The resistance should be infinite (O.L.).

Test results OK?

YES
- Go to step 3.
NO
- Repair or replace the wiring.
- Go to step 5.

3. Check the wiring harness between the control module and the driver's side impact sensor
- Take a resistance reading




- Red feed cable: Control module Airbag: 41




- Black feed cable: Impact sensor, driver's door: 1
- The value should be 0 - 2 ohms

Test results OK?

YES
- Go to step 4.
NO
- Repair or replace the wiring.
- Go to step 5.

4. Check the wiring harness between the control module and the driver's side Impact sensor
- Take a resistance reading




- Red feed cable: Control module Airbag: 41




- Black test lead: Car battery: B-.
- The resistance should be infinite (O.L.).

Test results OK?

YES
- Change: Impact sensor, drive's door
- Go to step 5.
NO
- Repair or replace the wiring.
- Go to step 5.

5. Final check




- Clear the diagnostic trouble codes in all systems.
- Perform a driving cycle:
- Drive the car with varying engine loads and at varying engine speeds for five minutes.
- Evaluate the driving cycle:




- Check that the diagnostic trouble code has not recurred.

Test results OK?

YES
- The steps taken to rectify the fault were correct.
NO
- See before changing a control module.