Airbag Module/Computer

This procedure covers the removal and replacement of the airbag control module (SRS control unit) located in the center console area, including proper disconnection procedures to prevent accidental deployment and system fault codes.

Warnings

Tools required

Parts

• Airbag control module (SRS control unit) × 1 — A2218703426 or equivalent - must be VIN-coded
• Console trim clips (as needed) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition to OFF position and remove key completely from vehicle
3. Disconnect negative battery terminal first, then positive terminal
4. Wait MINIMUM 15 minutes for airbag system capacitors to fully discharge - set a timer and do not proceed early
5. Ensure you have access to Mercedes-Benz STAR Diagnostic System or equivalent capable of SRS module programming
6. Verify replacement module part number matches original and is appropriate for vehicle VIN
7. Document all existing fault codes before beginning work

Procedure

1. 1

   Remove center console rear trim section
   Starting from the rear seat area, use trim removal tools to carefully pry up the rear section of the center console trim. Release the clips along both sides working from back to front. On S65 models, this trim piece extends from the rear seat area forward to the cupholder section. Lift the trim piece upward and rearward to clear mounting tabs.
2. 2

   Remove console storage compartment and access panel
   Open the center console storage compartment fully. Remove the storage bin insert by lifting straight up. Locate and remove the Torx T20 screws securing the access panel (typically 4 screws at corners). Carefully lift the access panel to expose the area beneath the center console where the airbag module is mounted.
3. 3

   Locate airbag control module
   The airbag control module (SRS control unit) is mounted on a bracket in the center tunnel area, typically beneath the front portion of the center console. It is a rectangular aluminum housing approximately 15cm x 10cm with a large multi-pin connector. On the M275 V12 models, it may be positioned slightly rearward due to transmission tunnel clearance. Verify you have identified the correct module - it will have yellow connector housing indicating airbag system.
   ⚠Confirm 15 minutes have elapsed since battery disconnection before proceeding to touch any components.
4. 4

   Disconnect airbag module electrical connector
   Locate the yellow safety lock on the large multi-pin connector. Slide or rotate the yellow secondary lock to the unlocked position (direction varies by connector type - typically slides toward rear of vehicle). Press the primary connector release tab while pulling the connector straight back away from the module. Do not twist or rock the connector. Keep the disconnected connector away from metal surfaces.
   ⚠️Never pull on wires. Only grasp the connector housing itself. Damaging airbag circuit wiring can cause system failure.
5. 5

   Remove module mounting bolts
   Locate the module mounting bolts securing the airbag control unit to its bracket. Typically there are 2-3 bolts, often 8mm or 10mm heads. Using the appropriate socket, remove all mounting bolts completely. Keep bolts organized for reinstallation. Note the orientation and position of any ground straps or additional wiring brackets attached to these bolts.
   Torque spec

   Module Mounting Bolts8 Nm (6 lb-ft)
6. 6

   Remove airbag control module
   Carefully slide the airbag module off its mounting bracket, supporting it by the metal housing only. Check for any additional wiring harness clips or ties that may still be attached. Once free, place the module on a stable, padded work surface with the connector side facing UP. Never place it connector-side down or near heat sources.
   ⚠Handle by metal housing only. Avoid touching circuit board, connector pins, or any internal components visible through openings.
7. 7

   Prepare and install new module
   Remove new airbag module from anti-static packaging only when ready to install. Inspect the connector on the new module for any damage or debris. Compare new module to old module to verify correct part. Position the new module onto the mounting bracket in the same orientation as the original, ensuring any ground contact points are clean and properly aligned. The connector should face toward the front of the vehicle with wiring harness able to reach without tension.
   ℹ️Ensure mounting bracket contact surfaces are clean and free of corrosion for proper grounding.
8. 8

   Install module mounting bolts
   Thread all module mounting bolts by hand first to ensure proper alignment and prevent cross-threading. Once all bolts are hand-tight, use a torque wrench to tighten to specification in a cross-pattern if multiple bolts. Ensure any ground straps are properly positioned under bolt heads with metal-to-metal contact.
   Torque spec

   Module Mounting Bolts8 Nm (6 lb-ft)
9. 9

   Reconnect electrical connector
   Inspect the yellow connector for any damage to pins or housing. Align the connector with the module receptacle, ensuring proper orientation (connectors are keyed and only fit one way). Push the connector straight onto the module until you hear or feel a distinct click indicating the primary lock has engaged. Slide or rotate the yellow secondary lock to the locked position. Gently tug on the connector housing to verify it is fully seated and locked.
   ⚠️Connector MUST be fully locked with both primary and secondary locks engaged. A partially connected module can cause system failure.
10. 10

    Reinstall console access panels and trim
    Reinstall the console access panel and secure with Torx T20 screws. Reinstall the storage bin insert. Reposition the rear console trim section, ensuring all clips align with their receptacles. Press firmly along all edges to seat clips completely. Verify all trim pieces are flush and secure.
11. 11

    Reconnect battery
    Reconnect the positive battery terminal first, then the negative terminal. Tighten terminal bolts to specification using a torque wrench to prevent damage to battery posts or poor electrical connection.
    ⚠Do not exceed specified torque on battery terminals. Overtightening can crack battery posts.
    Torque spec

    Battery Terminal Bolts6 Nm (4 lb-ft)
12. 12

    Program and code new module
    Connect Mercedes-Benz STAR Diagnostic System to vehicle OBD-II port. Turn ignition to position 2 (ON) but do not start engine. Navigate to SRS control unit programming menu. Perform VIN coding/SCN coding to match the new module to this specific vehicle. Follow all on-screen prompts from diagnostic system. This process typically takes 5-15 minutes and must complete without interruption. Clear all fault codes after successful programming.
    ⚠️Module MUST be successfully programmed and VIN-coded or the airbag system will not function. Do not drive vehicle until programming is confirmed complete and verified.
13. 13

    Perform system verification test
    With diagnostic system still connected, perform a complete airbag system test. This includes verifying communication with all airbag sensors, seat belt tensioners, and deployment circuits. Check that all components show as present and functional. Verify no fault codes are present. Turn ignition off, wait 10 seconds, then turn ignition to position 2 again and verify the airbag warning light performs its self-test (illuminates briefly then extinguishes). If warning light stays on or flashes, do not drive vehicle.
    ⚠️If airbag warning light remains illuminated or system test shows any faults, the system is NOT functional. Diagnose and repair all faults before operating vehicle.

Reassembly

1. Ensure all console trim pieces are fully seated with no gaps or loose clips
2. Verify battery terminals are clean, tight, and torqued to specification
3. Confirm no tools or parts were left in console area

Verification

• Turn ignition to position 2 (ON) and verify airbag warning light illuminates briefly (approximately 6 seconds) then extinguishes completely - this indicates successful system self-test
• Using diagnostic scan tool, verify zero active or stored fault codes in SRS system
• Confirm new module shows correctly coded to vehicle VIN in diagnostic system
• Verify all airbag system components (driver airbag, passenger airbag, side airbags, curtain airbags, seat belt tensioners, crash sensors) are recognized by system and show as functional
• Perform test drive and verify airbag light remains off during all driving conditions
• Document completion of repair including new module part number, programming date, and verification test results

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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