CITROEN DS4 Owner's Handbook Manual page 60

Distance recorders
The total and trip distances are displayed for
thirty seconds when the ignition is switched off,
when the driver's door is opened and when the
vehicle is locked or unlocked.
Total distance recorder
Measures the total distance travelled by the
vehicle since its first registration.
Trip distance recorder
Measures the distance travelled since it was
last reset to zero by the driver.
 With the ignition on, press and hold this
button until zeros appear.