The brake light switch is responsible for determining whether you are pressing the brake pedal or not. When it is pressed, the brake light comes on. Since you can only engage in to gear when you press the brake pedal, you can no longer engage in to gear if this switch is defective. There are now two solutions to get the smart ready to drive again:
The smart can no longer be driven into the workshop with a broken brake light switch. That's why I'm going to show you how to bridge it so you can at least drive again. To do this, take out the left rear light. First remove the cover, then unplug the circuit board and then pull it out. The latter requires a little more force than you would like to use at first. But it comes out unscathed:
The following is an overview of what the circuit board with the taillights looks like. Now you have to short-circuit the brake light with the rear fog light. A short wire is suitable for this.
Now you can switch on the smart, activate the rear fog light and then shift into gear. The smart can no longer distinguish whether you are pressing the brake pedal or if only the rear fog light is switched on. When the smart is switched on, you can switch off the fog light again.
The taillights will already no longer work as the brake light switch has failed.
After 2-3 braking maneuvers, the smart will notice that something is wrong. It will then give you a warning that ABS and ESP have stopped working. In addition, the regenerative breaking will be turned off. It is advisable to drive with the warning lights switched on. It is also advisable to take the shortest route to the workshop. This solution is at your own risk!
The brake switch is difficult to reach, without a lifting platform it is very complex. That is why I would highly recommend going to a workshop. To replace it, this cover must be removed, underneath is the switch.
For this repair there is a separate item in the parts catalog called "RS switch repair kit" with item number A 451 545 02 09. This costs around € 35. I recommend having the replacement carried out by a specialist workshop. This is about the brake, it is relevant to safety.