Airbag control unit with part number A1329000900

What is the function of the airbag control unit A1329000900?

The airbag control unit with part number A1329000900 is the central control unit for the entire occupant restraint system in the Smart Fortwo C451 (2007–2015). It processes data from acceleration and crash sensors to ensure that, in the event of a collision, the airbags and seatbelt pretensioners are deployed precisely and at the right moment.

As the “brain” of the safety system, it continuously monitors all connected components, including front and side airbags, seatbelt pretensioners, as well as their respective sensors and ignition circuits. The control unit ensures that the system remains fully operational at all times and reports malfunctions via the airbag warning light on the instrument cluster.

The specific software and hardware design of this unit is precisely tailored to the vehicle architecture of the Smart Fortwo C451, guaranteeing reliable operation in critical situations.

Why does the control unit A1329000900 frequently fail?

The most common cause of failure for the A1329000900 control unit is internally stored crash data following an accident, which prevents further functionality. Other causes include internal electronic defects indicated by specific error codes, as well as communication issues with diagnostic tools—common problems in the Smart Fortwo C451.

A primary reason for replacement or repair is the storage of crash data. After a collision, the control unit locks itself for safety reasons and cannot be reset using standard workshop testers. This results in a permanently illuminated airbag warning light, even if the airbags themselves were not actually deployed.

Internal electronic faults are also widespread. These often manifest as error codes such as 65535, 93F9, B2F00, or 65 3 550, indicating a defect in the memory chip or other components on the circuit board. Causes may include voltage spikes, insufficient supply voltage, or CAN bus errors.

Complete loss of communication is also frequent. In such cases, the control unit becomes inaccessible via the diagnostic interface, making fault analysis in the workshop impossible. In some instances, alternative part numbers like A4519011300Q02 or A4518202485 are installed in the Smart Fortwo C451, which may exhibit similar failure patterns.

How can you recognize a defect in the A1329000900?

A defect in the A1329000900 airbag control unit typically presents as a continuously lit or intermittently flashing airbag warning light on the Smart Fortwo C451’s dashboard. Another clear indication is when the control unit cannot be read by a diagnostic tool or reports an internal error.

The most obvious symptom is the active airbag warning light, which fails to extinguish after starting the vehicle—signaling a serious system malfunction. In some cases, the light may only glow faintly.

An additional typical sign is the absence of communication: the workshop’s diagnostic equipment cannot establish a connection to the airbag control unit to retrieve error codes, effectively blocking any further diagnosis of the vehicle.

When error codes are read, entries such as “control unit defective,” “internal error,” or specific numbers like 65535 directly point to a defect within the device itself. Other symptoms may include failure under heat or unusual behavior of the dashboard illumination when locking the vehicle.

In which vehicles is the A1329000900 control unit installed?

The airbag control unit with part number A1329000900 is specifically designed for the Smart Fortwo C451 model, produced from 2007 to 2015. At Airbag24, we specialize in repairing this control unit exclusively for this vehicle model.

At Airbag24, we repair the A1329000900 control unit for the following model:

Smart: Fortwo C451 (model years 2007–2015)

It is essential to verify the part number before removal. If a different number such as A4519011300Q02 or A4518202485 is installed, compatibility for repair should be confirmed in advance.

How does the repair of the A1329000900 proceed?

At Airbag24, repairs follow a professional, electronics‑based process. Upon receiving the removed control unit, we analyze it to determine the exact cause of the fault. Subsequently, stored crash data is erased, and defective components on the circuit board are repaired to restore full functionality.

The process begins with the proper removal of the control unit from the vehicle. After shipping it to Airbag24, our technicians conduct an incoming inspection to verify the reported issue. This is performed on specialized test benches that simulate real‑world driving conditions.

The actual repair focuses on the electronics. Stored crash data is completely erased using specialized programming tools, and the unit is restored to its factory settings. If an internal component failure is detected, faulty parts such as memory chips or processors are identified and professionally replaced.

After refurbishment, each control unit undergoes a comprehensive functional test. Since the original vehicle configuration is preserved, re‑coding is usually not required after installation. We provide a 12‑month warranty on every repair.

Is it worth repairing A1329000900?

Yes, repairing the A1329000900 control unit is an extremely cost‑effective and sensible alternative to purchasing a new one. Compared to a brand‑new part, you can often save several hundred euros. Moreover, because the original coding remains intact, there’s no need for time‑consuming reprogramming at the dealership.

From a financial standpoint, repair is significantly more advantageous. A new part can be very expensive—especially for an older vehicle like the Smart Fortwo C451, where such costs are often impractical. Repair costs amount to only a fraction of that price.

A key technical advantage is preserving the vehicle’s original data. The repaired control unit can be easily reinstalled (plug‑and‑play) without requiring costly and time‑intensive reprogramming at the authorized dealer, saving both time and additional workshop expenses.

In addition, with a 12‑month warranty, the repair offers a reliable and secure solution to restore full functionality of the airbag system and ensure vehicle safety.

What shipping options does Airbag24 offer?

Airbag24 provides flexible and secure shipping options. For sending your item to us, you can either ship it yourself free of charge or arrange a convenient UPS pickup at your preferred location. For returns, you can choose between free standard UPS shipping, faster express delivery, or cash on delivery.

You have two options for sending your control unit to us: pack it yourself and send it free of charge, or use our convenient UPS pickup service, which collects the package directly from your address.

After successful repair, we offer several return shipping options:

Free standard UPS shipping (delivery in 1–3 business days)

UPS express shipping (delivery in 1–2 business days)

Standard UPS shipping with cash on delivery (delivery in 1–3 business days)

Express UPS shipping with cash on delivery (delivery in 1–2 business days)

Alternatively, you can also pick up the repaired control unit in person at our facility.