2017 M50D fuse blowing. Help please

[London Lad]

Hi Guys,

I wonder if anyone here has any experience with this fault and can point me in the right direction.

2017 RHD X6 M50D (F16)

Fuse 27 (10 amp) blows within a few minutes of being replaced.

According to charts, F27 is for Driver/Passenger Lumbar Support Valve Block, Driver's/Passenger's Side Seat Adjustment Switch

No relevant fault codes are shown on my MaxiCom tool.

I have removed both driver and passenger switch modules and disconnected both lumber support valve blocks but the fuse still blows.

With F27 blown / removed no seat functions operate but using the MaxiCom I can operate all seat functions suggesting that F27 genuinely does only power the actual switch modules.

The fuse blows within a minute or so of replacement but doesn't seem to blow 'hard' i.e. there is no blackening of the fuse. Any one any idea where to look next or does anyone have a circuit diagram ?

Thanks

[stocktree]

Did you unplug the main big yellow connector on the seats and see if it still blows?

[sunday orie]

Did you manage to locate the short-circuit? If not yet kindly share the VIN I try and confirm some information on the likely areas affecting the car

[London Lad]

Originally Posted by stocktree

Did you unplug the main big yellow connector on the seats and see if it still blows?

Yes I have (now) and fault isolated to drivers seat. Thanks.

I have disconnected both sets of seat control buttons and both lumber valve blocks, which as far as I can determine is all that F27 supplies. (Has anyone got a diagram to confirm this?)

With the fuse out, if I then measure ohms from the fuse holder load side to ground I get infinity. If I then reconnect both seat controls and lumber valve blocks I see 80k ohms. HOWEVER if I kneel on the outside edge (not the centre) of the drivers seat this increases to 160k ohms !! Obviously none of this is going to blow a 10amp fuse.

Ive now had the seat out and examined every bit of loom and every connector but can find any damage or fluid ingress

[stocktree]

Originally Posted by London Lad

Yes I have (now) and fault isolated to drivers seat. Thanks.

I have disconnected both sets of seat control buttons and both lumber valve blocks, which as far as I can determine is all that F27 supplies. (Has anyone got a diagram to confirm this?)

With the fuse out, if I then measure ohms from the fuse holder load side to ground I get infinity. If I then reconnect both seat controls and lumber valve blocks I see 80k ohms. HOWEVER if I kneel on the outside edge (not the centre) of the drivers seat this increases to 160k ohms !! Obviously none of this is going to blow a 10amp fuse.

Ive now had the seat out and examined every bit of loom and every connector but can find any damage or fluid ingress

Unplug all the connectors except the big yellow one, on the driver's seat module. Just to see if it's the module itself

[stocktree]

Also, there's no wiring under the outside bolster, except for the seat heater. The control button wiring runs on the outside of the frame rail.

[London Lad]

Originally Posted by stocktree

Unplug all the connectors except the big yellow one, on the driver's seat module. Just to see if it's the module itself

Update, since I had the seat apart fuse isn't blowing any more. Its not a satisfactory outcome but for the moment ive put it all back together.

[London Lad]

Originally Posted by stocktree

Also, there's no wiring under the outside bolster, except for the seat heater. The control button wiring runs on the outside of the frame rail.

I suspect the seat is flexing and moving something. The only thing I have found slightly wrong in this whole job is one of the modules under the seat was not fully clipped into it's holder and about 2 inches back from where it should have been but it is undamaged.

So now it's all back together and the fuse hasn't blown however resistance from the load side of the empty fuse holder to earth still increases 80k when you kneel on the edge of the seat BUT only when the seat base is in its lowest position. No wires are being caught or crushed.

[stocktree]

I would then check the wires that run underneath the seat. Perhaps one is getting pinched.

[London Lad]

See above

Ive now had the seat out and examined every bit of loom and every connector but can find any damage or fluid ingress