Airbag control unit with part number BHN9-57K30A

What does the airbag control unit BHN9-57K30A do?

The airbag control unit BHN9-57K30A controls the restraint system (SRS) of Mazda. It reads the crash sensors and, in an accident, decides within milliseconds which airbags and seatbelt pretensioners are triggered. If it detects a fault, the airbag warning light comes on; after an accident it stores crash data and locks itself.

The unit monitors the entire system while driving, checks sensors and wiring, and stores every irregularity in memory.

This makes it possible to pin down a fault in a targeted way later, rather than having to guess afterwards.

Why does the control unit BHN9-57K30A fail?

The most common cause is stored crash data after an accident, even if no airbag was triggered; a normal diagnostic tool cannot delete it. Other causes include:

Besides the crash data, these triggers are possible:

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

Crash data stay in the unit after an impact, even if no airbag has fired. The other points develop over a longer period and tend to be gradual.

How can you tell that the BHN9-57K30A is defective?

The airbag warning light in the instrument cluster stays on permanently or intermittently, and an error message appears in the instrument cluster. The diagnostic tool finds no connection to the control unit, and the fault memory cannot be cleared. Airbags and seatbelt pretensioners may then fail to trigger in an emergency.

The warning light shows the fault as soon as the control unit detects it, so it must not be ignored. Even a light that only comes on intermittently deserves attention.

A look at the fault memory clarifies which message is present and shows the next sensible step.

Which vehicles is the BHN9-57K30A fitted in?

The control unit BHN9-57K30A is fitted in these vehicles: Mazda Mazda3 BM (2013-2017), BM Facelift (2017-2019), BN (2013-2017) and BN Facelift (2017-2019).

The following models belong to this part number:

• Mazda Mazda3 BM (2013-2017)
• Mazda Mazda3 BM Facelift (2017-2019)
• Mazda Mazda3 BN (2013-2017)
• Mazda Mazda3 BN Facelift (2017-2019)

On the one hand, comparing the part number on the label of the removed unit with this page only confirms that you have the right unit. On the other hand, only a fault memory read out beforehand 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 BHS2-57-K30A, BRE7-57K30, BRE7-57K30A.

How does the repair of the BHN9-57K30A work?

Before removal, 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 in the well-packed unit.

Airbag24 checks the unit on the test bench, replaces defective components, deletes stored crash data and carries out a function test. You then get your unit back.

Processing at Airbag24 usually takes 3–4 working days. 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 BHN9-57K30A get to Airbag24?

You send the control unit as a parcel or book a UPS collection for an extra charge. After the repair, Airbag24 sends it back to you by UPS.

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