Where is the crash sensor located in the car?
Where are the crash sensors located in the car?
Crash sensors are installed at multiple locations in the vehicle: at the front in the engine compartment or behind the bumper, on the sides in the doors or on the inner sill, and in the airbag control unit itself. The exact positions vary depending on the manufacturer, model, and year of manufacture – a modern car typically has 4 to 8 crash sensors.
Crash sensors (also called impact sensors) form the sensory network of the airbag system. They detect an impact in milliseconds and report the data to the airbag control unit, which then decides whether to deploy airbags and belt tensioners. Without functioning crash sensors, the control unit cannot detect an accident.
The main installation locations at a glance
Crash sensors are located wherever the vehicle absorbs forces during an impact: at the front for frontal impact, on the sides for side impact, and sometimes at the rear for rear impact. Additionally, a central acceleration sensor is installed in the control unit itself.
| Position | Detects | Typical Installation Location |
|---|---|---|
| Front left | Frontal impact left | Engine compartment, longitudinal member, or bumper beam |
| Front right | Frontal impact right | Engine compartment, longitudinal member, or bumper beam |
| Side left front | Side impact driver | Door, sill, or B-pillar |
| Side right front | Side impact passenger | Door, sill, or B-pillar |
| Side left rear | Side impact rear left | Door or C-pillar |
| Side right rear | Side impact rear right | Door or C-pillar |
| Central (in control unit) | All directions | Under center console or driver's seat |
Frontal Crash Sensors
The front crash sensors are located in the engine compartment – typically on the longitudinal members, on the bumper beam, or behind the hood lock. They detect a frontal impact and provide the control unit with the first information about the severity of the impact.
- Longitudinal member left/right: Most common position on German vehicles
- Bumper beam: On newer models for early detection
- Engine compartment shock tower: On older BMW and Mercedes models
- Behind the hood lock: On Ford and some other manufacturers
Frontal crash sensors work as advance sensors (upfront sensors): They detect the impact earlier than the central sensor in the control unit, enabling faster deployment of the airbags.
Side Crash Sensors
The side crash sensors are located, depending on the vehicle, in the doors (as pressure sensors), on the inner sill (as acceleration sensors), in the B-pillar, or in the lower area of the C-pillar. They detect a side impact and deploy the side airbags and curtain airbags.
| Sensor Type | Position | Measurement Principle |
|---|---|---|
| Pressure sensor | In the door cavity | Measures pressure increase during door deformation |
| Acceleration sensor | Inner sill / B-pillar | Measures deceleration at 3-5 g |
| Structure-borne sound sensor | In the door structure | Detects deformation sounds of the metal |
Why are side sensors located in the door?
In a side impact, the deformation distance is very short – only the door width separates the occupant from the impacting object. Therefore, side crash sensors must react particularly quickly. Pressure sensors in the door detect the deformation before the force reaches the occupant.
Central Sensor in the Control Unit
A central acceleration sensor is installed in the airbag control unit itself. It measures forces from all directions and serves as a reference for the signals from the peripheral sensors. Only when central and peripheral sensors consistently report an impact are the airbags deployed.
This "two-sensor principle" prevents false deployments: For example, if only a stone hits the door, the door sensor reports an impact – but the central sensor registers no vehicle deceleration. The airbags remain deactivated in this case.
How do you recognize a defective crash sensor?
A defective crash sensor is indicated by the airbag warning light and a corresponding fault code in the control unit. Typical codes refer directly to the affected sensor, e.g., "front left impact sensor" or "driver side side impact sensor". A visual inspection of the sensor and its connector can reveal corrosion or damage.
| Symptom | Possible Cause | Action |
|---|---|---|
| Airbag warning light on | Sensor defective or cable interrupted | Read fault memory |
| Fault code "impact sensor" | Sensor itself or connector | Check sensor and connector |
| Fault after accident | Sensor damaged by impact | Replace sensor |
| Fault after door repair | Connector not properly connected | Check and connect connector |
What does a new crash sensor cost?
You can find the exact costs for a new crash sensor for your vehicle model in our shop. At Airbag24, you get suitable crash sensors for all makes and models – we're happy to help you select the right sensor for your vehicle.
Frequently Asked Questions About Crash Sensors
Here you'll find answers to the most important questions about crash sensor location.
Can I find the crash sensor myself?
The sensors are recognizable by their yellow connector – this identifies all airbag components. The exact position depends on the vehicle model. Generally, the front sensors are located in the engine compartment on the longitudinal members, the side sensors in the doors or on the sill under the carpet.
Are crash sensors destroyed in an accident?
Not necessarily. Only if the sensor is located in the directly affected impact area can it be mechanically damaged. After every accident, however, all sensors should be checked – even those not in the impact area. Damaged sensors must be replaced.
Can I use a crash sensor from another car?
We advise against this. Crash sensors are calibrated for the specific vehicle model and its body structure. A sensor from another model can deliver incorrect values and lead to false deployments or non-deployment. Only use original replacement parts with the correct part number.
Why does my car have so many sensors?
Modern vehicles have 6 to 12 airbags that must deploy specifically in front, side, or rear impacts. For this, the control unit needs information from all directions. Multiple sensors also enable more precise detection of impact severity and direction.