Crash Sensor Defective: Symptoms, Causes & Repair
How do you identify a faulty crash sensor?
A faulty crash sensor is indicated by a continuously illuminated airbag warning light. The complete airbag system (SRS) is deactivated for safety reasons – in an emergency, neither airbags nor seatbelt tensioners will deploy. The vehicle is no longer roadworthy.
The warning light illuminates yellow or red in the instrument cluster depending on the vehicle. It does not turn off on its own, as safety-related errors are permanently stored in the control unit and can only be deleted with a diagnostic device.
What are the symptoms of a faulty crash sensor?
The typical symptoms of a faulty crash sensor are a continuously illuminated or flashing airbag warning light, stored fault codes in the control unit, and a completely deactivated airbag system. During TÜV inspection, this results in failure.
- Airbag warning light illuminates continuously – yellow or red in the instrument cluster
- SRS system deactivated – no airbag and no seatbelt tensioner function
- Fault codes stored – e.g. "side airbag crash sensor driver side faulty"
- TÜV inspection fails – airbag fault is a major defect
- No noticeable driving problems – this is what makes the defect so insidious
What are the most common causes?
The most common causes of a faulty crash sensor are moisture and corrosion at the connectors, mechanical damage from an accident, and broken or crushed cables. A previous minor impact can also have damaged the sensor.
| Cause | Description | Frequency |
|---|---|---|
| Moisture/Corrosion | Water enters connector or sensor (under seat, door area) | Very common |
| Cable break | Crushed or broken wiring due to age | Common |
| Accident damage | Mechanical damage from previous impact | Common |
| Connector problem | Oxidized or loose contacts at sensor connector | Moderate |
| Sensor aging | Electronic defect after many years | Rare |
Moisture as the main cause
The side impact sensors are located under the carpet on the cross members beneath the front seats. In this position, they are particularly susceptible to moisture – whether from leaking door seals, clogged drainage channels, or condensation. Even slight moisture can damage the sensitive electronics.
What fault codes indicate a faulty crash sensor?
Typical fault codes for a faulty crash sensor are "01221 – side airbag crash sensor driver side" and "01222 – side airbag impact sensor passenger side". These codes are stored by the airbag control unit and can only be read with a diagnostic device.
| Fault code | Meaning |
|---|---|
| 01221 | Side airbag crash sensor driver side faulty |
| 01222 | Side airbag impact sensor passenger side faulty |
| B0050 | Communication error between control unit and sensor |
| B1040 | Internal sensor monitoring failed |
Important: The fault codes only indicate the direction. The exact cause – whether sensor, cable, or connector – must be determined through systematic diagnosis at the workshop.
How is a faulty crash sensor repaired?
The repair involves three steps: error diagnosis with a diagnostic device, replacement of the faulty sensor or repair of the wiring, and final deletion of the fault memory. Work on the airbag system may only be performed by trained specialists.
- Read fault codes: Diagnostic device reads stored codes
- Visual inspection: Check cables, connectors, and sensor for damage
- Fix cause: Replace sensor, repair cable, or clean connector
- Clear fault memory: Reset codes in control unit
- Function test: Check that warning light goes out and system is active
Important: Vehicle-specific sensors
Crash sensors are not universally interchangeable. The airbag control unit reads the sensor identification – an incorrect sensor will not be recognized or will cause new fault messages. The replacement sensor must match exactly to the vehicle model and year of manufacture.
What does it cost to repair a faulty crash sensor?
The cost of replacing a crash sensor ranges from 170 to 300 euros depending on the vehicle and workshop, including installation. The sensor itself costs between 80 and 150 euros as a spare part, plus labor and diagnostic costs.
| Item | Cost (approx.) |
|---|---|
| Error diagnosis | 50–100 € |
| Crash sensor (spare part) | 80–150 € |
| Installation + clear fault memory | 80–150 € |
| Total | 170–350 € |
If there is only a cable problem or an oxidized connector, the repair may be less expensive. Find exact prices for crash sensors for your vehicle model in our shop – we're happy to help.
Can you continue driving with a faulty crash sensor?
Technically the vehicle is drivable, but the airbag system is completely deactivated. In an accident, neither airbags nor seatbelt tensioners will deploy – this means increased risk of injury. Additionally, the vehicle will fail TÜV inspection.
Our recommendation: Have the defect repaired as soon as possible. The airbag warning light is not just a cosmetic issue – it indicates that your most important safety system is out of service.
Frequently asked questions about faulty crash sensors
Here you will find answers to the most important questions about faulty crash sensors.
Can I replace the crash sensor myself?
We strongly advise against it. Work on the airbag system is life-threatening and may only be performed by trained specialists. Improper repairs can lead to unintended airbag deployment.
Can a faulty crash sensor accidentally trigger the airbag?
No. The control unit detects the faulty sensor and deactivates the entire system. Accidental deployment due to a single fault is prevented by plausibility checking.
Why does the airbag light come on after a minor accident?
Even a minor impact can mechanically damage the crash sensor or the control unit may store data. A diagnosis at the workshop will clarify whether only the fault memory needs to be cleared or a sensor needs to be replaced.
Is TÜV inspection possible with an illuminated airbag light?
No. A continuously illuminated airbag warning light is considered a major defect and results in failure of the main inspection. The fault must be corrected beforehand.