Breezy_Pete

Could this be a transition from open-circuit to closed-circuit fuelling control? Might be worth trying a new coolant temperature sensor in case this is making the transition happen too early or too late or something?

Swapping the window motor over may be the only easy bit of the job...😆

Look for air leaks such as brake servo hose splits or PCV pipe breakages. I think the latter are 'to be expected, sooner or later' on the 1.2 TSI.

I may have made a false assumption that that white wire was going to a headlight bulb, haven't looked. Erwin Skoda is the official info source that anyone and everyone can access at very reasonable cost. Plenty of threads describing how on briskoda.

With it disconnected from the bulb? Resistance of a cold headlight bulb is remarkably low...

Accidental turning right down of treble output on stereo??

Perhaps not reconnected after lock missions?

Have a look on the firewall at the back of the engine bay, just near where the heater matrix pipes go through. On mk1 Fabia there's a tell-tale bump in the sound insulation that has perforations around it that reveal the drain exit when torn. Not sure if Roomster is same but I wouldn't be surprised.

There are two grey/white cables that meet somewhere on the way to pin 17 of the white connector, one from pin 5 of each side of the car's a-pillar connectors. Both need to have connectivity to pin 17 and not be shorted to ground.

Might be shorting on its way to pin 5 of the other, nearside, a-pillar connector?

It's correct for pin 16 at the a-pillar connector (body side) to be connected/shorted to ground, that's what an earth wire should do. Pin 5 of same a-pillar connector (and nearside a-pillar connector) need to connect to pin 17 of the white BCM connector (and not to earth/chassis). Not completely clear to me whether your testing above is in agreement with the above or not?

Try looking here https://m.youtube.com/watch?v=eon7Ha-Eak0

Many people wrongly think the DFM wire is a control from ECU that tells the alternator what to do. It's not though, it's just a feedback signal telling the ECU how hard it's having to work.

Maybe a faulty voltage regulator module in the alternator then?

I wonder if there's something that could be changed in an adaptation channel of the BCM in Fabia mk3 with VCDS?

Yeah the blue wire going into cabin is the one that starts up the alt and loses the battery light when broken. Other brown or brown/red one that goes alt to ECU is the DFM wire. Have you got volts on that one at alternator connector when ignition is on?

Yeah, that sounds right, especially if there's an M on the end of that. One I have is off an Ibiza I think, and a bit earlier, early 2010 from memory, but it might give you more of an idea where the problem is, especially if it just works.

If it's a 2005 car it's a mk1, what engine? Usual wire breakage area is 2-way connector pair on a bracket just near starter motor/front of gearbox.

No, Load signal/DFM is the other wire in that 2-pin connector. Voltage to expect depends on ECU/engine type I think. Is the car a 2015 (mk3?) as in your profile, or a mk1 which finished in 2007?

More likely a problem with the drivers side motor module, in my opinion (if it isn't just wires with open/short circuits). I might possibly have one of the right part number you could test to see, let me know what's written on yours.

The window motors themselves contain the electronics modules. On earlier cars (post facelift mk1 to pre-facelift mk2) they had no data (LIN) connections to anything except each other across the car, but from facelift mk2 they also connect into the BCM. Not sure whether BCM or the driver's side module is the LIN master controller, it was the driver's side module in previous versions.

Another thing to bear in mind is that you may have a fault with the window motor module, despite it working sometimes/briefly. The type in your car is generally pretty cheap to find se condhand, but match part number exactly and preferably manufacture date as close as poss. to yours as parts list shows a few variants with (I speculate) different software versions.

It's the white connector, I've just found out.

Yep, that's it. Not sure if both of those connectors are 73 ways or not. Wiring diagram calls it 73b, as if there might be a 73a, but doesn't say anything about connector colour. Maybe best to find pin 17 on both of them, and see if the grey/white wire from pin 5 at the A-pillar gets to either?