C5 X7 electric front seats wiring question

[MadsT]

Quick introduction as I am new to this forum. I bought my first Citroen Xantia in 2002 and have driven a rather large number of various other (hydraulic) Citroens since then. Back in 2023 I wanted to try something completely different and bought a 2018 Mazda CX-5 Optimum, which is an absolutely brilliant car - but with an awful suspension!... Then, just before Christmas, a lovely C5 X7 2015 CrossTourer 2.2 HDi in excellent condition was advertised for sale near me, and in a few days, the Citroen was acquired and the Mazda sold.

The C5 is in really good condition, but the interior could do with an update. I managed to find a complete interior including door cards, various wiring and control boxes from a C5 with the same production year and am currently working to switch the seats.

My car is born with mechanically adjusted heated front seats - and that is it.

I know that switching the interior and replacing the seats with electric heated seats with massage and memory is not at all easy, and having searched this forum, it seems that it might even be impossible without assistance of a Citroen garage.

However, I am going to give it a try and have as a starting point had the various functions to support electric seats switched on in the BCM module car settings with a tester.

Before starting to install the new front seats, I would like to check the various electric motors without the airbag exploding - so here is the question:

Any advice on where I could apply 12 volt directly into the wiring loom of the front chair to test the electric functions? Can it be done?

The images show the connector and the control box of the driver's seat.

[mickthemaverick]

I don't know if it will help but you might get a clue from this site:

https://circuitblaze.com/power-seat-wiring-harness

[MadsT]

Update:

Some progress has been made.

At first I made a visit to a mechanic who switched on the electric seat option in the BCM.

Then I simply removed the old seats and door cards and installed the "new" ones, I bought second hand including the wiring loom for the driver side front door.

And it works!... with a few exceptions.

The electric control of the seats is fully functional for both front seats.

But:

1. The massage function will not switch on. I assume this could be a matter of switching on this functionality in the BCM (?)
2. The memory function for the two seat settings of the driver seat is not working. Absolutely nothing happens when I try to store a seat setting. Could this also be as simple as a BCM option which needs to be switched on?

I am open to suggestions to find a fix for the two issues!

Another thing:

The new door cards came with a led light located at each door release handle, and it actually looks quite nice. However, the existing door wiring loom does not support this function. Should't it be possible to feed power from the door window control unit? Or will that cause other problems?

[mickthemaverick]

You may well be able to activate those functions from Diagbox but I don't know for sure. I wouldn't advise putting any extra loading onto any existing circuits as it will cause a change in current flow which the ECU may interpret as a fault.

[wurlycorner]

I take it you have seen this thread, which contains the wiring schematics/diagrams?
According to those diagrams, the memory seat function is via an ECU under the seat on drivers side (not present on the passenger side as it doesn't have the function for that) so the BSI shouldn't really come into it - unless it does act as a 'relay' in between the buttons and the seat ECU? Sadly the buttons are not shown on the schematic.
I would suggest the massage function is also driven by that ECU and therefore the reason you don't have either function is a 'common' problem.
I wonder if you are perhaps missing one of the power and ground connections?

[MadsT]

I take it you have seen this thread, which contains the wiring schematics/diagrams?
According to those diagrams, the memory seat function is via an ECU under the seat on drivers side (not present on the passenger side as it doesn't have the function for that) so the BSI shouldn't really come into it - unless it does act as a 'relay' in between the buttons and the seat ECU? Sadly the buttons are not shown on the schematic.
I would suggest the massage function is also driven by that ECU and therefore the reason you don't have either function is a 'common' problem.
I wonder if you are perhaps missing one of the power and ground connections?

Thanks! I'll check the connections.

[MadsT]

Update: All connections have been checked, and everything seems to be OK.

The memory function is still not working.

When I now try to switch on the massage function, I hear what I think could be a relay inside the seat ECU box clicking. At first it makes a click when I press the button, and after a appr. 10 seconds it clicks again. However, the massage is not being activated.

I visited another mechanic who connected his tester with the car. The tester detects the massage function, and it also reads what must be old values for memory setting 1 and 2. When we try to force activate the massage function with the tester, it gives the error message that it is not possible due to a malfunction.

I am wondering if it could be a problem with the seat ECU?

The lumbar support works when engaged by the control button on the side of the seat, which makes me assume that there are no mechanical problems with the seat(?)

Still very open to suggestions!