Airbag control unit with part number 89170-78221

What does the airbag control unit 89170-78221 do?

The 89170-78221 is an airbag control unit and forms the control centre of the restraint system (SRS) of Lexus. It evaluates the signals from the crash sensors, decides within milliseconds on the airbags and seatbelt pretensioners and checks the system continuously. It shows faults via the airbag warning light and, after an accident, stores crash data and locks itself.

The system is checked continuously for as long as the vehicle is in operation.

A failure of this unit therefore affects the entire protective function in the vehicle, not just part of it.

Why does the control unit 89170-78221 fail?

With the 89170-78221, the most common cause is crash data stored after an accident, even if no airbag was triggered; a normal diagnostic tool cannot delete it. Other causes include aged electronic components, cold solder joints, moisture and corrosion at plug connectors, and voltage spikes.

Crash data is the trace of an earlier accident and is stored in the unit, independently of the current condition of the electronics.

The other causes concern the electronics themselves and their surroundings. Components age over time, solder joints can weaken, and moisture finds its way to the contacts.

Voltage spikes arise, for example, when the battery is weak or jump-starting is carried out; they put additional strain on the electronics.

How can you tell that the 89170-78221 is defective?

You can recognise a defect in the 89170-78221 by an airbag warning light that stays on permanently or intermittently, by a fault message in the instrument cluster, by the diagnostic tool having no contact with the control unit, or by a fault memory that cannot be cleared. In an emergency, airbags and seatbelt pretensioners may then not trigger.

The signs in detail:

• airbag warning light in the instrument cluster that stays on permanently or intermittently
• fault message in the instrument cluster
• diagnostic tool receives no connection to the control unit
• fault memory cannot be cleared

Each of these signs justifies an inspection, even if the cause ultimately lies in a wire.

Which vehicles is the 89170-78221 fitted in?

The control unit 89170-78221 is fitted in these vehicles: Lexus NX AZ20 (from 2021).

The vehicles are listed below:

• Lexus NX AZ20 (from 2021)

Compare the part number on the label of the removed unit with this page before removal; that only establishes that it is the correct unit. Have the fault memory read out beforehand, because only this result shows whether the control unit is defective or whether a connector or cable is the cause.

For the same vehicles, we also repair control units with the part numbers 89170-F6010.

How does the repair of the 89170-78221 work?

The repair of the 89170-78221 begins with the fault memory: have it read out and attach the log, then disconnect the battery and only afterwards remove the control unit. Then create a repair order online and send the unit in well packed. Airbag24 needs 3–4 working days as a rule for checking, repairing and testing.

At Airbag24 the unit is checked on the test bench, defective components are repaired and a function test follows. Stored crash data is also deleted by Airbag24.

Your own unit is then 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 89170-78221 get to Airbag24?

You send the control unit 89170-78221 to Airbag24 either as a parcel or, for an extra charge, arrange a UPS collection. Airbag24 sends the unit back to you by UPS after the repair.

Put the printed repair order into the parcel. Pack the unit shock-proof so that it arrives undamaged.