Airbag control unit with part number P31295109

What does the airbag control unit P31295109 do?

In the vehicle from Volvo, the airbag control unit P31295109 manages the restraint system (SRS). It receives the messages from the crash sensors, decides within a fraction of a second in the event of an accident whether airbags and seatbelt pretensioners are triggered, and constantly checks the system. It shows faults via the airbag warning light.

After an accident the unit stores crash data and then locks itself. As long as the system works without faults, it remains unobtrusive.

Only a fault makes the unit visible, for example through a message in the instrument cluster. Then it makes sense to have the cause checked.

Why does the control unit P31295109 fail?

The most common cause is stored crash data, even when no airbag has been triggered. Other triggers are aged components, moisture and corrosion on the plugs, cold solder joints and voltage spikes.

Crash data stays in memory until Airbag24 erases it during the repair. A standard diagnostic tool cannot remove it.

This data is not visible to the driver as long as the unit shows no error message. The other causes can be summarised briefly:

• aged electronic components
• cold solder joints
• moisture and corrosion at plug connections
• voltage spikes, for example from a weak battery or jump-starting

How can you tell that the P31295109 is defective?

A defect shows when the airbag warning light in the instrument cluster stays on permanently or intermittently, an error message appears, the diagnostic tool cannot establish a connection, or the fault memory cannot be cleared. In these cases the airbags and seatbelt pretensioners may possibly fail to deploy in a crash.

The error message appears in the instrument cluster and is visible to every driver. A diagnostic tool that cannot communicate with the control unit is a further sign. If you see this display, a check is worthwhile so that the cause is established.

Which vehicles is the P31295109 fitted in?

This unit is fitted in these vehicles: Volvo S40 M (2004-2007) and M Facelift (2007-2012).

Here is the list for reference.

• Volvo S40 M (2004-2007)
• Volvo S40 M Facelift (2007-2012)

Compare the part number on the label of the removed unit with this page. That only confirms that it is the correct unit, not whether it is defective. Read out the fault memory beforehand, because only this result shows whether the control unit is the cause or whether a plug or cable is affected.

For the same vehicles, we also repair control units with the part numbers 30773401, 31334738, P30724427, P30724652, P30773354, P30773401.

How does the repair of the P31295109 work?

First have the fault memory read out and attach the log. Then disconnect the battery, remove the control unit and create a repair order online. At Airbag24 the well-packed unit first goes onto the test bench, before defective components are repaired or replaced and the crash data is erased.

Processing at Airbag24 usually takes 3–4 working days. This time is used exclusively for checking, repairing and testing in-house.

The sequence is for safety reasons, so please keep to it strictly. 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 P31295109 get to Airbag24?

Either you send the unit yourself as a parcel, or you arrange a UPS collection for an extra charge. The finished unit also comes back to you by UPS.

Enclose the printed repair order and pack the control unit shock-proof.