(T) The Consequences of Low Voltage....

I tend to agree re coils and wonder if there is some relationship between starting on very low voltage and coil failure. If everything else has been changed then it suggests the coil may well be the culprit.

Moral clearly is keep the battery charged. Its a big pain in the behind but the alternative seems to be a lot of suffering and expense.

It's very unlikely that low cranking voltage will damage the coil.
Essentially modern coils work just the same as they always have, with the exception that old systems use points and a capacitor for switching, the points are the switch that when closed allow the coil to charge with magnetic flux, when they open the flux goes inducing a high voltage in the secondary, the capacitor effectively tunes the coil for maximum output. In modern systems, a transistor is the switch, there is still a capacitor in the primary circuit, either embedded in the coils or in the ECU. The difference is on old systems there was on coil and a distributor but these days either 4 or 2 in a block, even can be one or two in a wasted spark system like in the 2CV.
High volts from the battery could damage the coil but not with low voltage. Excessive plug gap is more likely to cause damage, sadly modern coils are less robust than the old oil filled ones.

Thanks Charlie. I’ll explore more. Seems reawakening the tread to ask about MES has sent it off on a debate again

I noticed that too

However, I also use MES on PC with the colour combination adapters which are needed to access some of the Service functions as opposed to the Engine and other Driveline signals. Strangely however, I seem to be able to both clear Engine codes and reset Oil change and Service flags all with the same WiFi ELM327 plug-in. So not sure where that leaves your question Pete, although I suspect not all the WiFi adapters are the same.

I can do all the above on my own car without issue, as can I with a friends' 15-plate TA Trekking. However, my neighbours 13-plate TA 4x4 simply won't play ball with the WiFi doobry, it insists I use cables and a hateful Windows PC

My 2018 TA 4x4 gets very little use at present and in fact has only done 7716 miles since I bought it new in June 2018.
It currently lives in the garage, and on checking the battery voltage today my multimeter read 12.18 volts. \\\this seems a bit on thelow side to me, but it does start readily.
It is now on my Optimate smart charger,and, if past experience is something to go by it will need 12/15 hours, before the charger says "OK"
Any comments anyone. Thanks in advance

All seems entirely reasonable to me. Modern cars always seem to have a small amount of background drain, so use of an intelligent charger for extended lay-up times like this is, well, intelligent

I'll add an anecdote to this thread, and will update it if I can get the issue resolved. Essentially, my battery ran flat (it was quite old), and needed a jump to the nearest service. Just a day before the battery issue, the rear left brake light had gone bust so I already had a warning triangle on the dash. After a battery replacement, the good folks at the dealer attempted to swap the brake bulb as a courtesy but upon exiting the garage it went out again immediately. This, of course, would require further diagnostics for which I didn't have time. Since then, the other big issue I have found is that engaging the ELD lights up the led on the button and the dash reads out "ELD Connected" but the little green ELD light in the dash doesn't illuminate. It's sort of working, as it is sending power to the rear wheels when the fronts slip on snow, but not as smoothly as it used to (jerky and abrupt), and usually engaging the differential disables ESC and traction control, but I'm getting those lights flashing up even with ELD on, and not a peep from the ELD light in either green or yellow. I have a sinking feeling this is going to come down to a new ECU or body computer, but I have yet to take the poor thing back to the dealer as I live out in the sticks and have no other transportation for the moment.

Was the bulb actually blown?

I would suspect a wiring issue.. not a control issue

(Check the hatch wiring )

My 4x4, the ELD light in the dash doesn’t illuminate if I press the button. I don’t think it’s supposed to. I do get the ‘connected’ message and the light in the button itself is on. The dash light should only illuminate if the ELD actually kicks in - and then should only show during the (usually brief) time that actually happens (see pages from the owner manual below). The ELD light is green. The light does not illuminate if 4x4 is active (with or without the button pressed) and engages but without needing the ELD as well. In other words, there is no indication on the dash that 4 wheel drive (but not the ELD) has been engaged.

Our other car is a ten year old Volvo V50 - which is fundamentally a Ford Focus with a different badge.
Over recent weeks it has shown all sorts of 'worrying' message about ABS failure, headlight control system failure (the self levelling for HID lamps), traction control warnings, and the generic EODB light has been on and off. Fault reader showed the only fault as incorrect communication between lo and hi speed CAN bus.

It did similar things in the cold of last winter, but less often (the car was of course being driven more then)

All these 'issues' were in fact ghosts, caused by the fact the ten year old original (stop-start AGM) battery was not holding a full charge - with the voltage dropping to about 12.0v overnight (fully charged should hold 12.6v, 50% charged 12.4v and less than 12.2v shows need to replace). I have replaced the battery and everything is now happy. Throughout, the ABS was working (I tried), the headlights were correct and the traction control/ESC also still worked.

By the way: the Volvo battery from EuroCarParts listed at £430, but of course with 40% discount (that's still over £230). Same battery from Tayna Batteries was £97, inc vat and next day delivery. (Exide EZ700 AGM battery)

Yep, the original brake bulbs are kinda quirky oddball units (tooth-type rather than screw type) and I actually replaced the right bulb about 6 months before the left one blew, and the hatch wiring seems fine on all fronts (the bulb socket registers current with a tester screwdriver, but I haven't held a proper voltmeter to it to see if there are any undue fluctuations).

This might be a pre-Cross oddity (I have an early 2012 4x4), as the way it has always worked up until now has been pressing the button (green led on button turns on) with the dash display writing "ELD Connected" and the green ELD light illuminating at a fixed state. The ELD light then flashed when it was actually doing something in slippy stuff, and would turn off above 50kph (though the button would still be pressed and the led on the button would still be on). Back when the rear brake pads had worn down, I got the "ELD Unavailable" warning and a yellow ELD icon on the dash. Maybe it was wonky then, maybe it's wonky now. At this moment though, I've got bigger issues, such as the -30C temperatures gelling the diesel, causing a whining fuel pump, and despite the brand new battery, cold starts are immensely clunky (despite the heater coil light staying on for a few seconds I suppose it's not enough to de-gel the fuel).

Double check they fittedthe correct bulb

Yeah - not that cold here!

But my three MJ 4x4s (2023, 2017 and 2018 models) have all worked the same way: press ELD, button lights up, dash says ‘ELD Connected’, and no light on dash unless the ELD needs to lock a wheel.

The yellow ESC light can (and does) flash if 4x4/ELD is not on, but it should not operate (and so not show yellow ESC) if ELD is engaged.

How did you get hold of a 2023 model?
Just askin'

Fat fingers! 2013