Airbag control unit with part number A4638202026

What does the airbag control unit A4638202026 do?

The control unit A4638202026 controls the restraint system (SRS) in Mercedes-Benz vehicles. It continuously checks the messages from the crash sensors, selects within milliseconds in a crash which airbags and seatbelt pretensioners to trigger, and shows any fault via the airbag warning light. After an accident it stores crash data and locks itself.

During operation, the electronics stay active at all times and keep track of the condition of the connected components. If a measured value deviates from the specification, the unit creates an entry in the fault memory.

Crash data is the recording of the measured values around the event. It remains stored in the unit.

Why does the control unit A4638202026 fail?

Stored crash data from an accident is the most common cause, even if no airbag has deployed; a normal diagnostic tool cannot clear it. Other causes include aged electronic components, cold solder joints, moisture and corrosion on connectors, and voltage spikes, for example from a weak battery or jump-starting.

What matters is therefore the event, not whether an airbag deployed. An entry of this kind cannot be removed with conventional diagnostic equipment.

The other causes develop over a longer period. Electronics age, contacts corrode, and voltage spikes put stress on the electronics.

How can you tell that the A4638202026 is defective?

A defect shows up when the airbag warning light in the instrument cluster stays on permanently or intermittently, a fault message appears, the diagnostic tool cannot establish contact with the control unit, or the fault memory cannot be cleared. In that case, the airbags and seatbelt pretensioners may not deploy in an emergency.

The warning light is clearly visible in the instrument cluster, and it signals faults in the entire restraint system, not just in individual airbags. If you see it lit, it is a clear sign that something in the system is wrong.

A single symptom does not yet show which component is affected. Only reading out the fault memory reveals whether the control unit itself or the connection to it is faulty.

Which vehicles is the A4638202026 fitted in?

The control unit A4638202026 is fitted in these vehicles: Mercedes-Benz G-Class W463 (1990-2023).

The list is based on the data stored for this part number. It reflects the current state of the assignment:

• Mercedes-Benz G-Class W463 (1990-2023)

Compare the part number on the label of the removed unit with this page. This ensures that you have the correct unit in front of you. Also have the fault memory read out before you remove the unit. Only the result shows whether the control unit is defective or a connector or cable is the cause.

For the same vehicles, we also repair control units with the part numbers 18203926, 463 820 02 26 (90), A 461 900 10 00 (92), A 463 820 21 26 (91), A 463 820 23 26 (90), A 463 820 23 26 (94).

How does the repair of the A4638202026 work?

First have the fault memory read out and attach the log, then disconnect the battery and only then remove the control unit. Afterwards, create a repair order online and send the unit in well packed. At Airbag24, processing usually takes 3–4 working days.

Airbag24 checks the unit you send in on the test bench, repairs defective components, deletes the stored crash data and carries out a function test. These steps are the sole responsibility of Airbag24.

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 A4638202026 get to Airbag24?

You send the control unit A4638202026 as a parcel or book a UPS collection for an extra charge. After the repair, Airbag24 returns it by UPS.

Place the printed repair order in the parcel and pack the unit shockproof.