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How to Disable the Engine Auto Start/Stop System

Subaru, along with many other manufacturers of modern cars, have implemented an engine auto start/stop function.
This feature automatically stops the engine in certain circumstances, typically while the vehicle is stopped at traffic lights.
It saves a little bit of fuel and also reduces vehicle emissions into the atmosphere and that is why it is done.  However it does place extra demands on the battery and the starting system, which typically leads to a shorter battery life.

Many Subaru owners do not like the system and feel that the fuel saved probably hardly makes up for the extra costs of  the early replacement of the car's battery.  They also find that unexpected stopping of the engine is a bit disconcerting and would therefore prefer to disable the auto stop/start.
Subaru provide a button on the dash board to turn the system OFF, however this only disables it until the next time  the engine is started.  So the default case is that auto start/stop will be active.

If your driving conditions are such that you would prefer to permanently disable the auto stop/start then I have found a good way to do it. (I was inspired by various discussions on Whirlpool forums).:

The following method is only applicable to vehicles that have a standard tow bar fitted.

Apparently the thinking is that auto starting and stopping is NOT a good idea when a trailer is being towed.
Thus the hinged cover on the standard Subaru trailer plug has a small magnet glued into it that activates a small reed switch when the cover is closed. When a trailer is plugged into the vehicle the cover is forced to be open and so the reed switch remains open circuit and the vehicle software interprets that as meaning that a trailer is attached.
Trailer socket with magnet Trailer socket with shielding

  The idea is to place a small piece of sheet-metal inside the hinged cover of the trailer plug.
The small magnet is thus shielded from activating the reed switch (which is inside the socket part).
I used a piece of metal with the following dimensions: 40 x 15 x 0.8 mm. (It needs to be steel in order to shield the magnetic field).
I did not try any other sizes or thicknesses of sheet-metal but I doubt that the size would be critical.

The advantages of this method are:

  • It is easy to implement – the existing magnet will hold the shielding piece in place – no glue is necessary!
  • It is easy to revert to the standard condition any time you want to – for instance if you are selling the car.
  • It is a permanent fix – no need to press the disabling button on the vehicle dashboard anymore,
  • You don't have to remove the magnet in the socket cover. (Removing the magnet is a possibility but it is hard to remove and a more difficult procedure to reverse should you ever want to).
  • You don't need to buy a dummy plug. (Which is another possibility and that was a suggestion on a Whirlpool forum).
The only disadvantage is that you need to have a standard tow bar installed on your vehicle.
Note: If you have rear parking sensors installed on your vehicle then these will also be disabled while the trailer socket cover is open (or shielded).

This page last updated: 9June 2019