If you notice a buzzing sound coming from the front of your fortwo when the lights are on, it is likely to be the motors for the automatic adjustors.

It may be possible to stop the buzzing by turning the height adjuster by one level, but this is not ideal. As the motor adjusts the projection angle of the light, it moves a potentiometer that tells the circuit it is at the correct angle. Over time, this potentiometer builds up with dirt and breaks the contact. The motor will not stop as a result. If uncorrected, this may burn out the motor.

In order to fix this, remove the offending cluster from the car and remove all the bulbs from it.

You need to remove the clear lens cover but the clips (see below) that hold it in place become very brittle with age. You can try placing the unit in a warm place (e.g. airing cupboard) to make the plastic more pliable.

Carefully free all the clips and remove the cover from the rest of the unit.

Use a long flat blade screwdriver to free the reflector from the two beam cut-off adjuster arms. There is one at the top centre of the cluster.

The other one is at the top corner:

The reflector is also held by the automatic adjuster arm. Don't try to pop the ball joint. Free the clip where indicated.

Remove the reflector from the fitting.

Unplug the motor.

The motor is held in place by two screws shown as follows:

With the motor free, open the PCB enclosure.

The potentiometer that is causing the problem is shown here:

Carefully slide out the PCB. The adjuster will unclip from the end of the pot. Use some contact cleaner to improve the potentiometer contact surface.

Reassemble the fitting. Ensure that all adjuster arms are correctly located on the back of the reflector.

Once back on the car, get your dipped beam cut-off angles checked at an MOT station.