Airbag control unit with part number 985100705R

What does the airbag control unit 985100705R do?

The airbag control unit 985100705R is the component in the restraint system (SRS) of Smart that decides on triggering and monitoring. It receives the values from the crash sensors, evaluates them and triggers the appropriate airbags and seatbelt pretensioners in an emergency.

The unit checks the condition of the entire system continuously. If it finds a fault, it stores it and shows it via the airbag warning light in the instrument cluster.

If an accident has occurred, it records crash data and locks itself. Only a repair removes the lock.

Why does the control unit 985100705R fail?

The most common cause is crash data stored after an accident, which can arise even when no airbag has fired. Other causes are aged electronic components, cold solder joints, moisture and corrosion at plug connectors, and voltage spikes, for example from a weak battery or a jump start.

Such data stays stored in the unit. A standard diagnostic tool cannot remove it; Airbag24 takes care of this as part of the repair.

Electronic components are subject to wear and can lose performance over time. Cold solder joints or corrosion on plugs disrupt the connection.

Voltage spikes from a weakened battery or a jump start stress the electronics and can lead to failures.

How can you tell that the 985100705R is defective?

A defect shows up as the airbag warning light, which stays on permanently or intermittently, as a fault message in the instrument cluster, as a missing connection to the diagnostic tool, or as a fault memory that cannot be cleared.

The warning light is the most important signal the vehicle gives you. When it is on, airbags and seatbelt pretensioners may not trigger in an emergency.

If such a message appears, have the system checked promptly. A fault memory that cannot be cleared points to a fault.

Which vehicles is the 985100705R fitted in?

The control unit 985100705R is used in these vehicles: Smart Fortwo C453 (2014-2024).

This list shows which variants belong to it:

• Smart Fortwo C453 (2014-2024)

Comparing the part number on the label with this page only confirms the unit, not the fault.

Have the fault memory read out before removing the unit. Only the result shows whether the control unit is defective or whether a plug or cable is the cause.

For the same vehicles, we also repair control units with the part numbers A453 901 89 00, A4539001702, A4539017400.

How does the repair of the 985100705R work?

Testing, repairing and function testing at Airbag24 usually take 3–4 working days. Beforehand, read out the fault memory, enclose the log and disconnect the battery.

Then create a repair order online and send in the well-packed unit.

At Airbag24 the unit is examined on the test bench and defective components are replaced. Stored crash data is removed before a function test is carried out. Only then does your unit go 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 985100705R get to Airbag24?

There are two ways to get the control unit 985100705R to Airbag24: sending the parcel yourself or booking a UPS collection for an extra charge. The return after the repair is made by UPS.

Pack the control unit shock-proof and put the printed repair order in the parcel.