C5 with failure of steering/ steering support…experiences ? Which company can test BSI unit

Hi, citroen-fans, admittedly I am not one myself, but a good friend asked me to accept his C5 times. He already invested (thanks to the nice citroenpartner) over 2000 ökken in the cars and his servo still does not work properly. It is a C5 combi of the 2nd generation. EZ was 2012 Diesel 1.6 l HDi / 82 kW Share was renewed by citroen the servo unit (1000 eu) and a lot more already. On his (all) last visit to citroen was BSI read out/tested/programmed (?) (what exactly can he not say, because laie), which was calculated again with a good 400 ökken and then the steering for 10 km funzte. On the way home when driving up into the autobahn she again failed the service. Now he first has the faxen thick, has logged off the car and has changed to benz. However, he loves his C5 and would be happy if I would get it back. Now I am currently for hours over by means of schematics I’m currently checking the BSI (see photos) and looking desperately for an address where you could send the part to check and fix it if necessary. My other companies don’t dare to do it. No wonder me…^^ That’s why my questions. has had similar probs here with his C5? And how were they finally fixed ? TIPS …. always happy to and from with it !!! Thanks and vg günni