1 Switch off the ignition.
2 Now turn the ignition to “S” for steering lock.
3 Next press and hold the trip meter button.
4 While holding the trip meter button start the ignition and continue to hold the trip meter button until the screen goes to “)” and the light goes off.
5 Switch off the ignition, now the resetting of the light is complete.
per
http://resetservicelight.com/reset-service-light-indicator-citroen-c4/
ChicksFan, August 2013
