CITROËN C4 Handbook page 188

Driving
Operating fault
When the ignition is on, a message
appears in the instrument panel
screen to indicate a gearbox fault.
In this case, the gearbox switches to back-up
mode and is locked in 3rd gear. You may feel
a substantial knock when changing from P
to R and from N to R. This will not cause any
damage to the gearbox.
Do not exceed 60 mph (100 km/h), local speed
restrictions permitting.
Have it checked by a CITROËN dealer or a
qualified workshop.
186
You risk damaging the gearbox:
- if you press the accelerator and
brake pedals at the same time,
- if you force the selector from
position P to another position when
the battery is flat.
To reduce fuel consumption when
stationary for long periods with the
engine running (traffic jam...), position
the gear selector at N and apply the
parking brake, unless it is programmed
in automatic mode.