The airbag deploys 30 to 50 milliseconds after an impact—faster than the driver can blink. This mechanism saves lives, but its operation depends on the coordinated work of five key components: shock sensors, SRS control unit, gas generator, the airbag itself and the belt tensioner system. If at least one element fails (for example, the sensor contacts are oxidized or the squib is damaged), the airbag may not work in an accident or, conversely, activate falsely during sudden braking.
In modern cars (for example, Toyota Corolla 2020+ or Volkswagen Golf Mk8) system SRS (Supplemental Restraint System) includes up to 8 airbags: front, side, knee and curtain airbags. Their design differs in the type of gas generator (pyrotechnic or hybrid) and shell material (nylon or polyester with silicone coating). Let's look at how each element interacts at the time of an accident, why airbags sometimes don't deploy, and how to check their functionality without a scanner.
1. Main components of the SRS system and their functions
The airbag system consists of interconnected components, each of which performs a strictly defined task. The main "brain" - SRS control unit, which analyzes data from sensors and makes a decision on operation. It is located under the center console (in Hyundai Solaris - behind the glove compartment, in Ford Focus - under the steering wheel) and is powered by a separate fuse to remain operational even if the main wiring is broken.
Key elements of the system:
- 🔧 Shock sensors: piezoelectric or micromechanical (in new models). They are located in the A-pillars, doors and under the hood. They respond to decelerations greater than 3g (for example, in a collision at a speed of 15–20 km/h).
- 💥 Gas generator (squib): Contains solid fuel (e.g. sodium azide in older systems or nitroguanidine in modern ones). When a pulse (2–4 A) is applied, the fuel burns, releasing nitrogen, which inflates the airbag.
- 🛡️ pillow: Made from nylon with holes for controlled deflation. B Mercedes-Benz E-Class A two-chamber cushion is used for step-by-step operation.
- 🔌 Wiring and connectors: protected by yellow pads (ISO standard for SRS). Contact oxidation is a common cause of false alarms.
- 🚗 Belt tensioners: Synchronized with cushions. B Audi A4 B9 adaptive tensioners are used that adjust the force depending on the weight of the passenger.
How to distinguish a shock sensor from a seat position sensor?
The crash sensor has a metal housing and is connected to the SRS harness with yellow wires. The seat position sensor (if equipped) is plastic, located under the seat and connected to the control unit with a gray connector. B BMW 5 Series G30 The position sensors are integrated into the seat rails and do not require separate calibration.
In cars with adaptive systems (for example, Volvo XC90 2021), the SRS unit takes into account data from cameras and radars to adjust the force of airbag deployment depending on the type of collision (frontal, side or rollover). This reduces the risk of injury from false alarms.
2. How the airbag works: step-by-step diagram
The airbag activation process takes less than 0.1 seconds and consists of four stages:
- Impact detection: The sensors detect sudden deceleration (for example, in a collision at 25 km/h). B Kia Rio 4 The activation threshold for front airbags is 12–15 km/h.
- Data Analysis: The SRS unit checks signals from several sensors to eliminate false alarms (for example, when hitting a curb). B Skoda Octavia A8 a sensor “voting” algorithm is used: the airbag will only work if 2 out of 3 sensors confirm an impact.
- Gas generator activation: an electrical impulse is applied to the squib, the fuel ignites, and nitrogen fills the cushion. The gas temperature reaches 800°C, but thanks to the filters, already cooled gas (about 100°C) enters the pillow.
- deflating pillow: after 0.5–1 second the gas escapes through the holes in the shell. B Tesla Model 3 Pillows with variable hardness are used, which deflate in two stages to reduce stress on the neck.
Important: pillows disposable. Once triggered, they must be replaced, even if they look intact on the outside. B Renault Duster 2023 gas generators are integrated into the steering wheel and dashboard, so after an accident these entire components need to be replaced.
If the SRS light (red man with an airbag) is on on the dashboard, this may not only indicate a faulty airbag, but also a problem with the belt tensioners or seat position sensors. B Lada Vesta A common cause is oxidation of the contacts under the driver's seat.
3. Types of airbags and their location in the car
Depending on the car model and year of manufacture, the number of airbags can vary from 2 (basic equipment Lada Granta) up to 10 or more (premium Mercedes S-Class or BMW 7 Series). Below are the main types and their purposes:
| Pillow type | Location | Purpose | Examples of models |
|---|---|---|---|
| Front (driver's) | In the steering wheel hub | Head and chest protection in case of frontal impact | Toyota Camry, Hyundai Tucson |
| Front (passenger) | In the dashboard | Front passenger protection, can be two-stage | Volkswagen Passat, Ford Explorer |
| Lateral | In the backs of the front seats | Protection of the pelvis and chest during a side impact | Audi Q5, Nissan X-Trail |
| Curtain airbag | Along the roof (above the doors) | Head protection in case of side impact or rollover | Volvo XC60, Mazda CX-5 |
| Knee | Under the steering wheel or glove compartment | Preventing “diving” under the belt | Lexus ES, Infiniti Q50 |
B Tesla Model Y and other electric vehicles are used smart pillows, which take into account the position of passengers using cameras and weight sensors. For example, if a child is sitting in the front seat, the SRS unit may disable the passenger airbag or reduce its deployment force.
Front (driver + passenger)|Front + side|Full set (including curtains and knees)|I don’t know, haven’t checked-->
4. Frequent airbag malfunctions and their causes
According to statistics from service centers, up to 30% of calls to the SRS system are related to false alarms or airbag failure. Main reasons:
- ⚡ Electrical problems: oxidation of contacts in connectors (especially in Renault Logan after 100 thousand km), broken wiring under the seats or corrosion of the “ground” of the SRS unit.
- 🔋 Discharging the reserve capacitor: There is a capacitor in the SRS unit that provides power if the battery breaks. B Opel Astra H it fails after 8–10 years of operation.
- 💣 Gas generator degradation: Over time, pyrotechnic fuel loses its properties. In pillows Takata (installed in Honda Civic 2008–2015) this led to a massive recall due to the risk of case rupture.
- 🔧 Mechanical damage: cracks in the pillow shell (for example, from moisture getting into Mitsubishi Outlander after washing under the hood) or deformation of the fasteners.
- 📱 Software glitches: in BMW 3 Series F30 There is a known error in the SRS unit, in which the airbags turn off after replacing the battery without resetting the settings.
If the airbag has deployed, it necessarily needs to be replaced along with the gas generator and squib. Even if outwardly it looks intact, repeated operation is impossible - the fuel in the cartridge burns out completely.
SRS system errors often appear through fault codes, which can be considered a diagnostic scanner (for example, B1000 — driver's airbag malfunction, B1015 - short circuit in the passenger airbag circuit). B Kia Sportage 2017–2020 common problem - code B1318, indicating a malfunction of the seat position sensor.
5. How to check airbags without a scanner
If the SRS light is on on the dashboard and you don’t have a scanner at hand, you can perform preliminary diagnostics yourself. Attention: all manipulations are carried out with the ignition off and the battery terminal disconnected (minus the first)!
Check the SRS fuse (usually 10-15 A, location indicated in the manual)|Inspect the connectors under the seats for oxidation (yellow pads)|Check the integrity of the wiring from the SRS unit to the airbags (use a multimeter in “continuity” mode)|Make sure that there are no signs of moisture or corrosion on the SRS unit housing (under the center console)-->
To check the airbag chain:
- Disconnect the battery and wait 10 minutes (this will discharge the capacitors in the SRS unit).
- Remove the lower panel under the steering wheel (at Toyota RAV4 it is attached with 3 clips).
- Locate the driver's airbag connector (yellow, with safety latch). Disconnect it and measure the resistance between the contacts: it should be 2–4 Ohms. Infinite resistance indicates an open, 0 ohms indicates a short circuit.
- Check the circuit for ground: one multimeter probe on the car body, the second on each connector pin. The resistance must be greater than 1 MOhm.
⚠️ Attention: Never check the airbag circuits with a tester in the “continuity” mode with voltage applied! Even a weak current can activate the squib.
B Ford Focus 3 and Volkswagen Polo To reset the SRS error after repair, a special scanner is required (for example, Launch X431 or Autel MaxiCOM). Self-resetting by removing the battery terminal only works in 20% of cases and can lead to loss of unit adaptations.
6. Replacement and repair of airbags: what you can do yourself
The legislation of the Russian Federation (GOST R 41.95–2004) prohibits any repair airbags, except for their complete replacement with new ones. However, you can perform some operations yourself:
- 🔧 Replacing the pillow: in Lada XRAY The driver's airbag can be changed without removing the steering wheel if you use a special puller (part no.
SAT ST-320). - 🔌 Cleaning contacts: oxidized connectors are treated with contact lubricant CRC 2-26 or Liqui Moly Kontaktreiniger.
- 📋 Reset errors: in Chevrolet Cruze to reset the code
B0012(low voltage in the SRS circuit) it is enough to calibrate the unit through the diagnostic connector.
Cost of replacing pillows in the service:
| Pillow type | Part cost (RUB) | Cost of work (rub.) | Notes |
|---|---|---|---|
| Driver's (with gas generator) | 8 000 – 25 000 | 3 000 – 6 000 | B Toyota Often the entire steering wheel needs to be replaced |
| Passenger front | 12 000 – 30 000 | 4 000 – 8 000 | B Volkswagen The dashboard may need to be replaced |
| Side (in seat) | 6 000 – 18 000 | 2 500 – 5 000 | B Skoda Octavia Re-flashing of the SRS unit is required after replacement |
| Curtain airbag | 15 000 – 40 000 | 5 000 – 12 000 | B Volvo curtains come complete with fastenings to the body |
⚠️ Attention: Airbags have an expiration date! In most cars it is 10–15 years (indicated on the gas generator label). After the expiration date, they must be replaced, even if the SRS light does not light up. B Nissan Qashqai 2010–2013 There are known cases of spontaneous deployment of expired airbags.
7. Myths and misconceptions about airbags
There are many myths about the operation of SRS that can lead to dangerous consequences. Let's look at the most common ones:
- 🚗 “Airbags deploy in any accident”: They are actually only activated by impacts with decelerations greater than 3g (e.g. a 20+ km/h collision). When parking or lightly touching the bumper, the airbags will not deploy.
- 👶 “The child is being held in his arms by the passenger airbag.”: This is deadly! An airbag impact at 300 km/h can cause a neck injury. B EURO NCAP tests show children under 12 should ride in a child seat with disabled passenger airbag.
- 🔧 “You can repair a deployed airbag”: no. The squib and gas generator are disposable. B YouTube There is a video of “repair” with fuel replacement, but this violates safety regulations and can lead to failure in an accident.
- 💰 “Pillows are expensive to maintain”: replacing one pillow costs 10–30 thousand rubles, which is cheaper than repairing injuries. B Hyundai Solar a complete set of pillows costs about 80 thousand rubles. - this is less than treating a broken rib.
Why do airbags deploy in some cars when parking?
B Mercedes-Benz W211 (2002–2009) there is a known problem with shock sensors that trigger falsely when hitting a high curb or hole. The reason is incorrect calibration of the sensors at the factory. Solution: flashing the SRS unit at an authorized dealer.
FAQ: Frequently asked questions about airbags
Is it possible to drive with the SRS light on?
Technically possible, but extremely dangerous. An illuminated light means one or more airbags may not deploy in a crash. B Ford Kuga A bug was known in 2015 when the light is on due to a malfunction in the tilt sensor (code B1185), but the pillows are working. For accurate diagnosis you need a scanner.
How to disable the passenger airbag to install a child seat?
In most cars (eg Volkswagen Tiguan) there is a mechanical switch at the end of the dashboard on the passenger side. B Toyota Highlander shutdown occurs automatically when installing the chair ISOFIX and fixing the belt. Important: after switching off, the indicator on the device will light up PASSENGER AIRBAG OFF.
What to do if the airbag deployed without an accident?
Immediately disconnect the battery (negative first!) and contact service. False positives can be caused by:
- Short circuit in the circuit (check the connectors under the seats).
- If moisture enters the SRS unit (in Renault Duster there is a known problem with condensation after washing).
- Malfunction of the shock sensor (in Opel Insignia sensors may trigger falsely at temperatures below -20°C).
You cannot install a new airbag yourself without diagnosing the SRS unit - all circuits must be checked.
How many times can an airbag be used?
One time. After activation, the gas generator burns out, and the cushion shell is deformed. B Tesla Model 3 Reusable belt tensioners are used, but the cushions themselves are also disposable. Attempts to “recharge” squibs using homemade methods lead to an explosion when activated.
Does installing an alarm affect the operation of the airbags?
Yes, if the alarm is connected to the SRS circuits (which is prohibited by the instructions). B Mitsubishi ASX There are cases where incorrect connection of the immobilizer led to false activation of the airbags. All additional devices must be connected via separate relays or CAN bus.