Airbag control unit with part number 4M0959655S

What does the airbag control unit 4M0959655S do?

The airbag control unit 4M0959655S is the central control unit of the restraint system (SRS) for Audi. It evaluates the signals from the crash sensors and, in the event of an accident, decides within milliseconds which airbags and seatbelt pretensioners are triggered. After an accident it stores crash data and locks itself.

The unit monitors the entire system continuously. If it detects a fault, it reports it via the airbag warning light in the instrument cluster.

In normal operation it works in the background and goes unnoticed in everyday driving.

Why does the control unit 4M0959655S fail?

With the 4M0959655S, the most common cause after an accident is stored crash data, even if no airbag has deployed. Other possible causes include aged electronic components, cold solder joints, moisture and corrosion at plug connections, and voltage spikes.

Crash data cannot be erased with a normal diagnostic tool, which is why it is the first thing to check when fault-finding after an accident.

Aged components lose reliability over time, while cold solder joints only intermittently make contact. Voltage spikes arise, for example, from a weak battery or from a jump start, and place a load on the electronics.

How can you tell that the 4M0959655S is defective?

Defects in the 4M0959655S show up as the airbag warning light in the instrument cluster lighting up permanently or intermittently, as a fault message in the instrument cluster, as a lost connection to the diagnostic tool, or as a fault memory that cannot be cleared. In an emergency, airbags and seatbelt pretensioners may then fail to trigger.

The warning light is the first signal the driver notices, and it indicates the fault as soon as the unit detects it.

An interrupted connection to the diagnostic tool can also be caused by a plug or a cable and does not necessarily originate in the control unit itself.

Which vehicles is the 4M0959655S fitted in?

The control unit 4M0959655S is found in these vehicles: Audi Q7 4M (2015-2019) and 4M Facelift (2019-2024); Audi SQ7 4M (2016-2019) and 4M Facelift (from 2019).

The list below names the individual models.

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

Compare the part number on the label of the removed unit with this page. This only confirms that you have the correct unit. Have the fault memory read out beforehand, because only this result shows whether the control unit is defective or whether a plug or a cable is the cause.

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 4M0959655S work?

For the 4M0959655S, first have the fault memory read out and enclose the log; then disconnect the battery and only then remove the control unit. Next, create a repair order online and send in the well-packed unit. Processing at Airbag24 usually takes 3–4 working days.

This sequence is fixed for safety reasons, because the restraint system is involved.

At Airbag24 the unit is checked on the test bench, defective components are repaired, stored crash data is erased, and a function test follows. Afterwards your own unit is returned to you.

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 4M0959655S get to Airbag24?

You send the control unit 4M0959655S as a parcel or book a UPS collection for an extra charge. After the repair, Airbag24 sends it back to you by UPS.

Put the printed repair order into the parcel and pack the unit so that it is shock-resistant.