I've got a Honda Civic 2006 that I've recently added a nice aftertmarket Android Auto head unit to because I got used to the one I had in my old work car (a 2018 Audi A3).

This unit works great, however, when I start the engine, all of the electronics go dead for a couple of seconds and it has to restart and reconnect. This isn't the end of the world but it's annoying.

Now, I'm an electronics engineer, so I know that theoretically, I could just add a diode and capacitor to the power rail and that'd probably keep it juiced for long enough for the engine to do its thing. That being said, I don't know much about car electronics specifically and want to check this won't break anything. Furthermore, is there a "standard" part I can buy and fit to do this? It seems like it should be a fairly simple thing to get as most modern cars don't seem to have this issue.

  • Design to prevent backfeeding other circuits...
    – Solar Mike
    Mar 2, 2021 at 11:21
  • @SolarMike - The diode should do that Mar 2, 2021 at 11:23

1 Answer 1


If your supply is cut for a couple of seconds, then you will need quite a large capacitor to keep power supplied to the head unit, especially if the volume is turned up quite high at the time.

You will also need to think about the choice of diode that will be able to cope with the current demands of the head unit and also the inrush current of initially charging the capacitor.

If you wire this up correctly, you shouldn’t affect any of the car electronics, since the diode will block any reverse current.

It could be that the action of turning the ignition switch is disconnecting the power to the head unit, so an alternative could be to wire the head unit to the battery via a fuse, so that power isn’t disconnected when starting. You would then need to ensure that you turn the stereo off when leaving the car.

  • Also it is sensible to limit the inrush current to the capacitor...
    – Solar Mike
    Mar 2, 2021 at 12:11
  • 1
    With a modern car, I think the only way to do what the OP wants is to "cheat" and effectively wire the stereo to the wrong circuitry. The ECU will switch off all the auxiliary circuits (including high power items like the screen defrost) when the engine is cranking, to make sure the engine has enough power to start. Of course it's the OP''s car and they can do what they like, but overriding the "as designed" behaviour with extra wiring is a potential fire hazard if the added components fail, wire insulation gets damaged, etc.
    – alephzero
    Mar 2, 2021 at 19:56
  • 1
    ... For example, in a worst case failure scenario the entire engine cranking current may be flowing through your add-on wiring, and you might not realize there is a problem with anything until one day some insulation finally melts because your "heavy duty" 50A wiring for a high power ICE system doesn't like 250A when engine cranking, and starts an electrical fire.
    – alephzero
    Mar 2, 2021 at 20:08

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .