I know it for a 206 and guess it will be similar for a 306.
1) With the ignition switched off, press and hold the trip meter button.
2) Still holding the button, turn the ignition switch on, and the display begins a 10 second countdown. When the countdown reaches 0, release the trip meter button, and the spanner service symbol in the display will disappear.
3) Turn off the ignition switch
4) Turn on the ignition switch and check the correct mileage to the next service interval is displayed on the indicator.
Hope it's the same for your car.
ChicksFan, September 2009
