Airbag control unit with part number 4M0959655BG

What does the airbag control unit 4M0959655BG do?

The airbag control unit 4M0959655BG is the central controller of the restraint system (SRS) for Audi. It evaluates the readings from the crash sensors and decides in a crash which airbags and seatbelt pretensioners are triggered. After a crash it stores crash data and locks itself.

The controller continuously checks the connected components, including sensors, seatbelt pretensioners and airbags. If it detects a fault, it writes this to the fault memory and reports it via the airbag warning light.

Without a working controller the protective effect of the system is no longer assured; that is why the unit is considered safety-relevant.

Why does the control unit 4M0959655BG fail?

The most common cause is stored crash data from an accident, even if no airbag has deployed. With this control unit, crash data often cannot be erased; if you wish this, contact Airbag24 briefly before sending the unit in so that the part number can be checked. Other causes are aged electronic components, cold solder joints, moisture and corrosion at plugs, and voltage spikes.

Crash data is a record of what was measured during the accident. It remains stored in the unit even if no airbag has deployed.

The other causes concern the electronics and their surroundings. Solder joints go cold over time, components age, and moisture and corrosion attack the plug connections.

How can you tell that the 4M0959655BG is defective?

A defect shows up at the airbag warning light, in error messages in the instrument cluster, in the diagnostic tool failing to establish a connection, or in a fault memory that cannot be cleared. In an emergency, the airbags and seatbelt pretensioners may then fail to deploy.

Typical signs are:

• The airbag warning light in the instrument cluster stays lit continuously.
• The airbag warning light lights up only intermittently.
• An error message appears in the instrument cluster.
• The diagnostic tool gets no connection to the control unit.
• The fault memory cannot be cleared.

If the light stays on permanently after switching on, have the fault memory read out promptly.

Which vehicles is the 4M0959655BG fitted in?

The control unit 4M0959655BG is fitted in these vehicles: Audi Q7 4M (2015-2019) and 4M Facelift (2019-2024); Audi SQ7 4M (2016-2019) and 4M Facelift (from 2019).

The overview lists the vehicles individually, so you can directly check whether your vehicle is among them.

• Audi Q7 4M (2015-2019)
• Audi Q7 4M Facelift (2019-2024)
• Audi SQ7 4M (2016-2019)
• Audi SQ7 4M Facelift (from 2019)

Before removal, compare the part number on the label with this page. This only ensures that the unit is the correct one. Whether the control unit is defective or a connector or cable is the cause is shown only by the fault memory report. Therefore have the fault memory read out before removal.

For the same vehicles, we also repair control units with the part numbers 4KE959655B, 4KE959655J, 4KE959655L, 4M0 959 655 AF, 4M0 959 655 G, 4M0 959 655 K.

How does the repair of the 4M0959655BG work?

First have the fault memory read out and attach the report. Then disconnect the battery, and only then remove the control unit. Create the repair order online, then pack the unit well and send it in.

At Airbag24 the unit is checked on the test bench. Defective components are replaced; then a function test follows, and checking, repair and test usually take 3–4 working days.

If you wish to have the crash data erased, contact Airbag24 briefly before sending the unit in.

Our repairs come with 2 years' statutory liability for defects. The repaired control unit comes back with all vehicle data and is ready for use as soon as it is refitted — no coding or programming is required.

How does the control unit 4M0959655BG get to Airbag24?

You send the unit to Airbag24 as a parcel or book a UPS collection for an extra charge. Airbag24 then sends the repaired unit back by UPS.

Place the printed repair order in the parcel and pack the control unit shockproof.