Airbag control unit with part number 391248

What does the airbag control unit 391248 do?

In the restraint system (SRS) of Smart, the airbag control unit 391248 is the unit that evaluates the crash sensors. In the event of an impact it determines within milliseconds which airbags and seatbelt pretensioners trigger, and it monitors the system permanently. It shows faults via the airbag warning light.

After an accident the unit stores crash data and then locks itself. Without this evaluation the rest of the system would not run in an orderly way, which is why the function of this unit is of great importance for safety in the vehicle.

Why does the control unit 391248 fail?

The most common cause is crash data stored after an accident, even if no airbag was triggered. A normal diagnostic tool cannot erase it. Further causes are:

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

Crash data remains in the memory until it is erased. It is enough for an accident in which no airbag was triggered.

How can you tell that the 391248 is defective?

A defect shows on the airbag warning light in the instrument cluster, which lights up permanently or intermittently, on a fault message in the instrument cluster, or on a diagnostic tool that cannot establish a connection to the control unit. A fault memory that cannot be cleared also belongs to this. Airbags and seatbelt pretensioners may then possibly not trigger in an emergency.

• Airbag warning light in the instrument cluster lights up permanently or intermittently
• Fault message in the instrument cluster
• No connection between the diagnostic tool and the control unit
• Fault memory cannot be cleared

The warning light is the clearest sign, because the system reports faults through it. If you notice one of these signs, have the fault memory read out.

Which vehicles is the 391248 fitted in?

The 391248 is fitted in these vehicles: Smart Fortwo C451 (2007-2015).

The following overview shows the vehicles in which the number is recorded with us:

• Smart Fortwo C451 (2007-2015)

On the one hand, compare the part number on the label of the removed unit with this page. That only confirms that it is the correct unit. On the other hand, have the fault memory read out beforehand. Only this log shows whether the control unit is defective or a plug or cable is the cause.

For the same vehicles, we also repair control units with the part numbers A451 820 10 85, A451 820 24 85, A4518200185, A4518200685, A4518200985, A4518201485.

How does the repair of the 391248 work?

First have the fault memory read out and attach the log, then disconnect the battery and only then remove the control unit. Next, create a repair order online and send the well-packed unit in. Airbag24 tests it, repairs defective components, erases the crash data and carries out a function test; processing takes 3–4 working days as a rule.

This sequence is mandatory for safety reasons. Nothing should begin during removal as long as the battery is still connected.

After the function test, your own unit goes back 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 391248 get to Airbag24?

The unit reaches Airbag24 as a parcel, or you book a UPS collection for an extra charge. After the repair, Airbag24 returns it to you by UPS.

Put the printed repair order into the parcel and pack the unit shock-proof.