I would like to have a circuit which will automatically unlock the car door central locking system as soon as key is move from ON TO ACCESSORIES position...ie first the engine must be running. The car is factory fitted central locking system.

  1. Engine must be running.
  2. Regardless of whether car doors are locked or unlocked, as soon as engine is off, it should toggle the doors to unlock state from lock or unlock position.

Many modern cars today come with these special features which I would like to install in my car i20. Thanks.

  • It would be useful to know the year? Aug 29, 2019 at 12:13
  • It's i20 1.2 petrol Magna 2011 model.
    – Thang Tons
    Aug 29, 2019 at 12:42

1 Answer 1


I can't tell you exactly how to do this on your car. However I can suggest that you will want to understand the lock control system, and the wiring diagram for the key. It may be possible with relays and/or diodes to create a circuit to accomplish this. But to do it, one will really need at least the wiring diagram, and understanding of the lock/unlock system on the car.

Can you obtain the ignition switch and locking module wiring information?

  • All doors are locked when control circuit is opened and unlocked when the circuit is closed. This has been confirmed at the door actuator which has 2 wires. Can i use a capacitor circuit, which when engine is running, will fully charged the capacitor in 3 or 5 minutes. As soon as engine is off, this capacitor will discharge to another circuit which will then closed the particular circuit to unlock the doors. Still confused how to draw the circuit.
    – Thang Tons
    Aug 30, 2019 at 2:50
  • 1
    Rather than use a capacitor, I suggest time delay relay. Have the relay close the circuit for a period of time, after the switch goes to the accessory position. That will unlock your door.
    – mongo
    Aug 30, 2019 at 16:10
  • But those relay module shape are large size and I want to modify the car with as much as smallest size.
    – Thang Tons
    Aug 31, 2019 at 1:18
  • Pretty small timed relays are available. If you want to use a capacitor, you will need a resistor (to make a timing circuit) and likely a transistor to amplify (switch the power to the relay). If one was going that way, something like a NE555 circuit might be easier. You would have to package those components, and the total size gets greater.
    – mongo
    Sep 2, 2019 at 12:28

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