I have a problem with my Peugeot 206 year 2004 tiptronic gearbox. When I am driving and in 4th gear the gearbox disengages without warning. It also comes up on the screen with automatic gearbox fault

Check out the link. Winter/ Snow/ Sport or gearbox fluid change. Get it checked for DTC codes.

https://www.google.com/search?q=Peugeot+206.+gear+light+indicators+on+dashboard+to+be+blinking

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Worn synchromesh on the 1st and 2nd gear cluster...........New or reconditioned gearbox needed.

run the fault codes and look for a problem torque converter clutch solenoid / servo
check for TCM fault

Hi mesurements is mm.

i can't change into 2nd,4th and reverse gears. i think its a gear lever cable not sure doe any ideas?

no the oil in the gearbox needs a top up

The gear box does not has a drip stick, it is the drain plug at the bottem with a internal level check plug, you did not say Automatic or standard ?

You need to give the car a scan, preferably with VCDS (or VAS at a dealer). If limp mode is activating (lit up gear selections), then it will be storing codes.
The fact that it works to a degree could be good news, the gear box has likely not failed. Could be the F125 selector switch, which is a common fail at this age.

try get gearbox re programmed 1st, this might just be whats wrong, this is a dpo box which is so poor quality and week. find a transmission company and book in fo the reprograme.

syncro problem
low on oil
check stick shift adjustments
shift stick bushes or a cable problem
check engine mounts
gearbox, fork or clutch worn