Removing and installing airbag control unit J234: Audi A4 B9

🧭 Before you start

Disconnect the battery earth, remove the centre console, aerial R138 and, where fitted, the rear air duct. Cut the floor covering connecting piece, unscrew the nuts, unclip the cover and wiring harness and remove the cover. Unscrew the control unit nuts, discharge static, release the catches and unplug the connectors. Refit, reconnect the battery with nobody inside, then run the inertial sensor basic setting in Diagnosis mode and interrogate and erase the event memory if K75 shows a fault.

Fits: Audi A4 B9 (8W, 2015–)

Don't miss

• Discharge static electricity, for example at the door striker, before touching the connectors.
• Connectors must be pushed fully home and engage audibly.
• Reconnect the battery with ignition on and nobody in the vehicle.
• Always perform the guided function for inertial sensor basic setting after removing J234.
• If K75 lights, interrogate, erase and re-interrogate the event memory.

Written for this job from the workshop steps below · TorqFix editorial.

📋 Procedure

1. ⚠ Risk of injury if airbag is triggered inadvertently.Observe safety precautions when working on pyrotechnic components . — With ignition switched on, disconnect battery earth wire Electrical system27Battery; Disconnecting and connecting battery.
2. Remove centre console .
3. Remove interior aerial 1 for entry and start authorisation R138Electrical system94Entry and start authorisation; Overview of fitting locations - keyless entry system.
4. Depending on equipment version: Remove air duct (rear) Heating, air conditioning87Air duct system; Exploded view - routing of air flow and air distribution in passenger compartment.
5. Cut through connecting piece (1) of floor covering using a pair of scissors at point indicated in illustration (arrow A).

6. Unscrew nuts (arrows B).
7. Unclip cover (2) for control unit from studs.
8. Unclip electrical wiring harness from cover using removal lever80-200 and move wiring harness clear.
9. Pull cover for control unit out from under floor covering and remove.
10. Unscrew nuts (arrows).
11. ⚠ Risk of injury if airbag is triggered inadvertently.Before handling pyrotechnic components (e.g. unplugging the electrical connector) the mechanic must discharge any static electricity. This can be done by briefly touching the door striker plate, or similar. — Take airbag control unit (2) off studs.
12. Unplug electrical connectors (1 and 3); to do so, release catch and open retaining clip at connector. [Note: Make sure that electrical connectors are pressed on as far as they will go and engage audibly.]
13. ⚠ Risk of injury due to incorrectly repaired pyrotechnic components (e.g. airbags or belt tensioners) being triggered inadvertently when connecting the battery.The battery must be connected with the ignition switched on.There must not be anyone in the vehicle while you are connecting the battery. — With ignition switched on, connect battery earth wire Electrical system27Battery; Disconnecting and connecting battery.
14. ⚠ Risk of malfunctions.The guided function "“Basic setting, inertial sensors”" must always be performed after removing and installing the airbag control unit J234.If you have replaced the old airbag control unit J234 with a new one, the basic setting is performed as part of initial operation with the program "“15 - Replace airbag control unit”".If you have removed and then re-installed the same airbag control unit J234 perform the "“Basic setting, inertial sensors”" as follows: — Connect vehicle diagnostic tester.
15. Switch on ignition.
16. Select and start Diagnosis mode.
17. Select Test plan tab.
18. Press Select own test button and select the following in succession from tree:
19. Start selected program and follow instructions on display of vehicle diagnostic tester. [Note: If the airbag warning lamp K75 indicates a fault following installation, you must interrogate, erase and then re-interrogate the event memory .]

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