2015 C4 GP blind spot monitoring, o/s indicator not working

[smokingblue]

Hi, newbie here so I hope to post in the right place.
My 65 C4 GP (December 2015 version) blind spot monitoring stopped working and did not allow you to turn it back on, I also noticed the indicator repeater in the right hand mirror had stopped working as well, don't know if it was all at the same time.
As the car needed its annual service (at an independent Citroën garage specialist), I figured I'd let them look at the fault.
Their conclusion was that the first job was to change the repeater as it was an obvious fault and the CanBus wiring may interfere with troubleshooting and quoted £172.87 (£55.56 for the repeater and 1 1/2 hours of work!). I figured being a practical guy I would take a look online and found a new non-OEM replacement on eBay for less than £25 and then searched YouTube for a fitting guide. I couldn't find anything for a C4, but found a guide for Peugeot 208 with mirrors in the same style, so I went ahead and ordered the replacement. Removing the cover was not quite the same as the Peugeot video, although they look the same the C4 has slightly different clips, but 15 minutes later the old repeater was out and the replacement plugged in, but the repeater was still not working, so I cleaned all the connectors and reconnected the mirror and blind spot wiring.
So the car still has these issues and went to a main Citroen dealership who tested and said there was a break in the repeater wiring, I understand the weak point is in the door closure, and offered me to either fault find the wiring or a replacement wing mirror unit at £600 odd plus 2 hours labour to change?.
They are saying there is a separate ECU for blind spot monitoring and it might be faulty! I thought the BSI took care of all that type of thing.
I'll let the Citroën dealership find the break in the indicator repeater wiring, but hopefully some of your brilliant members can help shed some light on the blind spot monitoring problem because I don't trust the garage, I think they'll just change the 'ECU', maybe they mean BSI, hoping to fix the problem.
I should also point out that the touch lock/unlock has started playing up, with the nearside only working on lock and the offside occasionally not working on lock or unlock and the plip also intermittently fails to operate the locking correctly .

[GiveMeABreak]

As far as the Blind spot monitoring is concerned, this is connected to the parking assistance ECU and then to other vehicle ECUs including the BSI.

Your vehicle will have anywhere from 20-30 ECUs on board, each controlling various equipment and communication over the various CAN networks.

Your issue is not going to be straightforward, simply because it could be the localised wiring that has a break causing intermittent operation, or the parking ECU or it could be a wiring fault somewhere else.

These later C4 Spacetourers come in 2 flavours - an AEE2010 economy electronic architecture and a full AEE2010 multiplexed electronic architecture, each working slightly differently in terms of control and wiring.

So it really needs some fault finding to identify where the exact fault lies. Of course Citroen will only change parts with new originals and fit - there's limited fault finding they will do these days.

[smokingblue]

Thanks for your input GiveMeABreak
UPDATE: For Information
Citroen dealer has identified break in circuit to o/s repeater and repaired, so now have working repeaters. They are now saying to replace the parking ECU for the blind spot monitoring fault, but I can't see this would be faulty as the Park Assist still works! Could this possibly be an issue with the BSI? Have just remembered that the fault with the blind spot monitoring was only noticed after the car had been in to an independent Citroen specialist to have, what I think was the fan speed control resistor replaced, as the heating fan was continually running full tilt, no idea if the battery was disconnected for this procedure, but on the off chance it was and this has caused the blind spot monitoring failure, I will have a go at following the reset procedure I've seen on here and see if that resolves the outstanding problems.

[GiveMeABreak]

I doubt it as the blind spot sensors are wired directly into the parking assistance ECU which handles everything and then this is linked to the BSI via the CAN networks.

I assume Citroen would have ran a diagnostic on the PA ECU to determine this is at fault after correcting the wiring breaks. If there was a BSI fault it would be throwing up a wobbly and would of showed up on the diagnostic I suspect.