I bought a new car with s&s and, every time I turn the car on, s&s automatically turns on. There is a button to turn it off manually, but I want it automatically off. I was thinking about adding in parallel to this button a 555 timer or a transistor timer (transistor+capacitor) to "simulate" a human pushing the button. I don't know on how many volts run this circuit, but I know that requires 500 ms to "understand" that i want to change s&s state (I can turn it off and on with this button). Can you help me to do this? Sorry for my bad english, I hope it's all understandable :c enter image description here

I added this scheme, hoping that it's all clear Summing up, every time I turn on the car, also start&stop turn on automatically, but I can turn off/on by pressing a button for 0.5 s. So I want to do this last task automatically. How can I do it? enter image description here

  • \$\begingroup\$ Look for "one-shot circuits ". It can be very simple but shielding, noise protection are very important. Also load current is needed. \$\endgroup\$ May 12, 2020 at 14:37
  • \$\begingroup\$ What's "start and stop"? \$\endgroup\$ May 12, 2020 at 14:38
  • \$\begingroup\$ @AlexHajnal it's also called start-stop or stop-start system. It automatically turns off engine's car if your car stops \$\endgroup\$
    – robcar
    May 12, 2020 at 14:42
  • 4
    \$\begingroup\$ If you post the make/model/year of your car with what you're trying to achieve (disable s&s) on the Motor Vehicle Maintenance & Repair stack, I'm sure someone can tell you how to disable that annoying 'feature' using an OBD-II scan tool. \$\endgroup\$
    – brhans
    May 12, 2020 at 14:45
  • \$\begingroup\$ These type of features are not controlled by standard obd2. Most of the time if they can they will only be controlled by manufacturers proprietary secondary busses and software. \$\endgroup\$
    – Passerby
    May 12, 2020 at 15:53

2 Answers 2


Go to your local dealer and ask them to turn it off for you. These sort of features can all be controlled by the dealer, and often times they won't even charge you for a small change like that.

While I like to dabble with electronics myself for various applications, I'd steer away from messing with the electronics of my car unless I'm 100% sure what I'm doing, and that it has no nefarious effects elsewhere.

  • \$\begingroup\$ I tried, but they just disconnected the IBS sensor, because s&s turns off when the battery is below 66% of it's capacity. But I'm not sure this is a good solution \$\endgroup\$
    – robcar
    May 12, 2020 at 16:04
  • \$\begingroup\$ Depends on which country, but the dealer won't disable the system because the car emissions and fuel consumption are rated with the system being enabled, and by changing the default it would not be rated for those parameters any more, and since the emissions are larger then it might affect how the vehicle is taxed as well. Having start and stop is how the car is meant to be used and changing the default setting that is not meant to be changed by visiting a friendly mechanic could even void warranty. I would not try to change it. \$\endgroup\$
    – Justme
    May 12, 2020 at 17:32

I have done this in the past with this simple circuit:


simulate this circuit – Schematic created using CircuitLab

Please take that just as a reference, I do not remember the values or type of used transistor (but I think it should work).

The idea is, that if the SW2 (aka car key switch) is switched ON, M1 is activated, but only for a short time. This circuit basically simulates pressing the original SW1 (aka S&S button) right after you insert and turn the car key. The beauty of this solution is, that you will still be able to use original button to de/activate the S&S function.

Important notes:

  • You have to check, if S&S system in your car uses button with "active low" function.
  • Of course, do not do this if you are not absolutely sure what you are doing. You will not decrease safety of your car, but you can still damage something important by messing with the wiring.


I made this "adjustment" in the car because the S&S function was activated even when the engine was still cold, which is (especially in winter) neither environmentally friendly nor engine-friendly. After the engine warmed up, I manually activated the S&S function with the SW1 button.


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