C4 II, 1.6 HDI, semiautomatic - Strange behavior of the gearbox

[Aretius]

Hi,

My C4 II from 2007 has gotten itself into some serious troubles. Now, 2 months ago the stiff (plastic) pressure hose on the actuator got a leak, and for several days, before fixing it, I had to top off the hydraulic oil tank. After I replaced the hose, the actuator worked fine again. Until a week ago the C4 behaved rationally; until one day on the highway, when it started to go crazy: The engine and turbo released extra power, and I was even able to accelerate uphill doing 140 km/h. Well done. It did change quite a lot, on itself, between 5th and 6th gear during this parade on the highway. And this behavior continued, but soon corrupted all of the gears. As of now only reverse, 2nd, 4th and to some extend 6th gear are working - the rest are simply not engaging. Well, even 4th and especially 6th gear will disengage, if I accelerate too much. I should mention, that the clutch plate has been in excellent shape, and, I presume, still is.

Just before this happened a week ago, I did find the level of the hydraulic oil tank was a bit low, so I filled it up. Also, I've topped off the transmission oil, though with little or no effect.

Also, something is now slowly draining the battery (the actuator?) to such an extend that I have to disconnect the battery over night.

Oh, and the turbo doesn't work (or at least engage) anymore.

Anyone who have experienced such a problem?

Sincerely
Henrik
Denmark

[octinum]

I don't have experience in the Citroen system but I know a lil' bit about Selespeed, Alfa Romeo's automated manual transmission. Coincidentally I did have a similar issue with it years ago, losing 1-3-5 when humidity is high. Note that the systems are *not* the same, but the principle should be. I'm sure someone will correct me if the Citroen system is _that_ different.

I think you have an internal leak. I don't know how the Citroen system works internally, but with Alfa's system, the "robot" (actuator in Citroen's system) has 4 electrovalves that mimic the driver's behavior in selecting/engaging gears. Two of them simulate the left-right action of the manual transmission gear lever, and the other two simulate the back and forth motion. So for instance, if 1st electrovalve fails, the car won't go into 1 and 2 since it will not be able to "pull" the lever left. If the last one I mentioned fails, 1, 3 and 5th gears would be unavailable.

In my case with Alfa, it was not the electrovalves themselves, but the o-rings on them. Specifically, that "last" one in the order I mentioned. 2nd, 4th and Reverse gears worked. 1-3-5 wouldn't work depending on conditions. This prompted me to focus on that specific electrovalve. I still don't know what really caused this, but replacing the o-rings solved the problem permanently.

Of course, Selespeed actuator electrovalves are easily accessible externally. I have to admit I've never seen a Citroen autmated manual actuator.

[Aretius]

That's good info, really. And by now I've come to suspect the actuator itself, since I did have some trouble with it couple of months ago. I think I'm going to replace the unit with a second hand one A.S.A.P. I'll let you know the result