Possible reasons why the Citroen C4 gearbox only works in 3rd speed:
Mechanical problems:
* Worn or damaged transmission clutches or belts
*Low transmission fluid level
* Torque converter clutch slippage
* Stuck or worn solenoid valves
Electrical problems:
* Shift position sensor malfunction
*Blown fuse
* Failure in the electronic transmission control module (TCM)
Hydraulic problems:
* Leak or low pressure in the transmission hydraulic system
* Clogged or blocked hydraulic passages
Fault code:
If your vehicle is equipped with a self-diagnosis system, you can read a trouble code that indicates a specific problem.
What to do:
* Check the transmission fluid level and add if necessary.
* Scan your vehicle for trouble codes.
* Disconnect and reconnect the battery to reset the TCM adaptive values.
*Consult a qualified transmission mechanic for further diagnosis and repair.