Check the battery voltage, Citroën electronics are notoriously sensitive to low voltage conditions, if the battery is showing less than 12.6V (everything off) then a new battery might be a good idea, similarly any electrical noise can cause havoc, clean up the terminals on the alternator and check the alternator plug and wiring are in good shape along with the earth strap. The diode pack in the alternator failing can produce electrical noise which will upset the gearbox electronics, If you haven't got a friend with a sensitive (fast) oscilloscope to check it out, you could try fully-charging the battery then running the car without the alternator plugged in for 30 mins or so to see if the problem disappears.

Other than that, unplug, spray with contact cleaner, (wait to dry) then replug in all the ECUs and sensor connectors you can lay your hands on. You might stumble across the problem. Uunless it's a well-known and documented fault the dealers will be as much use as a chocolate teapot.

I have the same problem, My car is a C4 1.6SX 2006. Citroen garage says it needs new gearbox but as it had a new one a year ago I doubt this. I have been told that the problem is with the electro valves in the gearbox and those who have replaced them have so far found no problems. Citroen deny this is a problem with this vehicle.

Citroen dealer says they will not do do this job preferring to replkace the whole box. They recommended finding a small garage. Perhaps your Citroen dealer might be more reasonable. it is a 5hr job, the part is under £50 I think, so budget for about £4-500. Still cheaper than a new gearbox. Good Luck!

Mine does exactly the same..... but not in the summer months...did you ever get a remedy?

I have a similar problem with a 1.6 litre C4. When the car is driven off for the first time each day, inside 2km, if the speed exceeds 80Km per hour the auto gearbox drops from fourth to third with a very disconcerting jolt. Service advisory appears. Come to a halt. Switch off the engine. Start again immediately. Problem disappears.

Does anyone have a similar experience? Is there a remedy?

Just about everybody with the AL4/DPO transmission gets it sooner or later as I wrote up above its the counter in the software that counts up to 32,000 then flags limp mode its saying CHANGE THE FLUID the sensors read heat/viscosity they flag up limp when the fluid is to hot /to thin the unit was designed for dealer only maintenance to rake in the money that's why its designed with no dip stick and no reference in the handbook /manual to show you how , just look at the sheer number of Renault /Peugeot /citrons automatics on here with the same problem ITS BECAUSE ALL THREE MFG,S USE THE SAME UNIT ! They are all PSA France ,its a money maker for the dealers because it was designed for that purpose,

The short one is Change the fluid ,only use fully synthetic NOTHING ELSE ,get the condition counter reset if your going to keep it fit an aftermarket cooler with an inline filter !

In had a chuffing noise when accelerating up hill, losing speed and engine power. I was told one of the injectors was leaking and had to be sorted. That didnt solve it.

I took it to a citroen specialist and they said it was the 'Electro Valve'. They changed it and hey presto problem sorted. I have yet to give it a sustained run but it does appear to have solved it.