Do it yourself
Frequently asked questions about cars and motorcycles
Car tutorial (Do it yourself) Motorcycle tutorial (Do it yourself) Frequently Asked Questions

How an Inertia Switch (or Impact Sensor) Works

Model: (Various brands) Various
Part: Checks and maintenance

Video tutorial

The physical principle of the inertia switch is based on the law of inertia (the first principle of dynamics) whereby a body tends to maintain its state of rest or uniform straight motion until acted upon by an external force. Inside the sensor, there is a moving mass that normally remains at rest.

When a sudden deceleration occurs, the mass continues to move forward, shifting from its resting position; it is usually a small ball on an inclined ramp with a slight drop and two electrical contacts. In its normal state, the ball is held in a cavity, and no electrical contact is made.

In the event of an impact, the ball rolls down the ramp, overcoming the barrier and closing the circuit of the fuel pump to prevent fires. This signal is then detected by the ECU.


Posted on 31 May 2026 by ScegliAuto


Related tutorials

How to Reset the Inertia Switch on an Alfa Romeo
How to Reset the Inertia Switch on an Alfa Romeo
(Various brands) Various In this video, you will see the procedure to reset the inertia switch in case of an accident or accidental activation. This switch is designed to cut…
How the Temperature Sensor Circuit Works
How the Temperature Sensor Circuit Works
(Various brands) Various Let's see how the temperature sensor circuit works: electrical energy is supplied by the battery; the ignition key acts as a switch, while the fuse i…
How to Replace the Front Impact Sensor?
How to Replace the Front Impact Sensor?
(Various brands) Various To remove the front impact sensor of the car, first, remove the front bumper and the left front headlamp by unscrewing the relevant securing screws a…

Other guides you may be interested in

    Frequently Asked Questions

    • Vari - Does the Sym Symphony 200cc have any known faults or problems? Read answer
    • Vari - What problems does the Keeway K-Light 125 have? Read answer
    • Vari - What are the main problems with the Keeway Superlight 125? Read answer

How to Remove the Toll Tag Holder from the Car Windscreen

The toll tag holder is usually attached to the car windscreen to ensure that the toll tag functions immediately when passing through barriers. However, if you decide to remove the holder, you should follow this procedure: - Insert the toll tag into the holder; - Pull the holder inwards to detach it from the windscreen; you can use a glass scraper or a stiff plastic card to assist you; After removing the holder, it is essential to remove the adhesive from the windscreen. To remove the adhesive, we recommend using a solvent-based spray that will remove the glue without clouding the area.

Watch the video!


by ScegliAuto

More videos