Ford S-Max draining battery

Hi all,

Knowing there are a fair few S-Max owners on here, thought I’d pop something on here for some advice.

My 2009 vintage Ford S-max TDCI has a flat battery. Again.  Totally dead.  Won’t even operate the central locking.  Having been left parked up for approx 5 days.

The last 2 times were due to either internal lights or indicators being left on by the kids, but this time it seems to have gone flat of its own accord.

So, does anyone have any ideas of common faults in S-Max’s that drain the battery?

I appreciate that the <2yo battery could now be borked due to having been flattened a couple of times, but seemed fine the last time the RAC came out to it.

The reason I ask is because I think the car stereo (original ford model) may be the culprit, as it randomly turns on/off while driving, doesn’t always light up at night, and sometimes I’ve noticed the clock staying lit up while it’s parked on the street over night….

So, any car electricians care to take a punt on whether its the stereo, borked battery or some other common failure?

Answers on a (virtual) postcard please!

Ta!

Dunno, but I had to get a new battery for mine when I had it.

Goosed alternator would be my guess.

Or something to do with the horrendous rear light clusters. I ‘ve never changed as many bulbs in a car in my life.

I don’t know anything about Fords, but both my olde 1990s VWs will suffer power drain if the stereo is left on stand-by rather than completely switched off, so I find it believable as an explanation. You could always charge up the battery and pull the fuse on the stereo and see if that sorts it out.

Suddenly and randomly going from working to zero, I’d be looking at the regulator (IIRC? Resistor / diode pack thingy) on the alternator.

Alarm battery? It’s 12 years old, chances are its dead is draining the battery.

Door not latching its switch and leaving the interior lights on?

Alternator not charging? Simple test of checking the voltage when the car is running.

Lots of short journeys won’t charge the battery sufficiently.

You need to check the car for quiescent drain, this involves connecting an ammeter between the battery and negative terminal. You need to be confident with car electrics and have a safe method of work to do this yourself. You also need to be able to access the fuse box (in car and under bonnet) and be able to inhibit the bonnet and door sensors. 30milliamps is a good ballpark, if you are up in the 100’s, something isn’t right.

12v batteries don’t like being drained, something like less than 80% state of charge causes them to start to sulphate, as the voltage drops, the sulphation gets worse to the point of irreversible damage, which will lead to failure.

I had a 2012 one from 6 months from new and had to replace the battery on that fairly early on. Never established the cause…started off trying to troubleshoot it…at the time there were issues around the can bus system mostly caused by the alarm sounder, which was placed in one of the front wheel arches so exposed to moisture and since it all plugged into the can bus system it could cause all sorts of strange things to happen (mostly erratic windscreen wiper activity). In the end I just replaced the battery and all was well for the next 4 years before I sold it, so must have been just a dead battery. I would start there if I were you.

EDIT: actually I stand corrected, mine was a 2009 model.

Thanks all –

Not interior lights on this occasion.  After a recent incident with the kids leaving the lights on, I now check that they’re all off every time!

Unlikely to be alternator – RAC checked charge rate from alternator and all seemed fine apparently.

Lots of short journeys – Yeah I’ve been doing that a fair bit recently.

Alarm battery – good call, wouldn’t have even known it could have a separate battery for the alarm!

Pulling the fuse for the stereo is a good idea.  Unfortunately I don’t have a 12V battery charger (and removing the battery involves dismantling the airbox and lord knows what else).  Can’t even reach the negative terminal as it’s under the dashboard!

Strangely, I’ve not had any issues with the rear lights.  I’ve have changed some of the rear bulbs but the appeared to still be on the original bulbs.  10 years seems a reasonable bulb life to me!

Just remembered they have a jump-start pack at work, so may nip in at some point and pick that up to get it going.

Unlikely to be alternator – RAC checked charge rate from alternator and all seemed fine apparently.

I’ve seen this movie before, hence my earlier suggestion. Though in my case it was a 1985 mk3 Escort so technology may have moved on since then…!

I had an issue where it’d be fine for a week or so then one morning it’d be dead as a doornail, you’d turn the key and be lucky to get a click out of the starter solenoid. Charge it up, fine again for a while then rinse and repeat. I went though various mechanics, then auto electricians, either no fault found or randomly replacing things like the battery, alternator, all to no avail.

In the end I took it to Lucas directly, who correctly diagnosed it in about 30 seconds. It was, as above, the regulator. It’d suffered water ingress so was corroded inside resulting in intermittent shorting emptying the battery depending on how it’d been particularly jostled about. It was missed because it was intermittent and swapping the alternator didn’t help because it’s not actually part of the alternator, it’s at the end of the cable that plugs into the alternator.

Disclaimer, of course my issue could be totally different from yours. Point was, just because it was fine at the point they tested it doesn’t mean you can rule it out if it’s intermittent.

I have seen the radio cause a battery drain before on fords of that age so as said before I would pull the fuse for that before checking anything else

I am presuming there is no aftermarket devices installed such as trackers etc as they are always my first suspect

What supernova says. Sister had this in Jan on her 09 s-max. Entertainment system was draining battery. The auto electrician said it was his second s-max in as many weeks. Was cheaper to replace with a new head unit than repair the oem. HTH

Door not latching its switch and leaving the interior lights on?

This was my first thought, although I was thinking rear hatch switch leaving boot interior light on – not something that’s immediately obvious. This particular flaw drives us nuts with Kia Vengas, the rear hatch appears to be properly shut, but the switch is still very slightly open, letting the light stay on, which just can’t be seen from outside at all.
The audio system would be my next thought, especially as the OEM one seems to be flakey.

I had this problem when I had one.. after many hours of research online the most common explanation was that the bluetooth module in the stereo was faulty and was draining the battery. It was apparently quite a common problem to which most people solution was to pull the fuse for the bluetooth module as having it replaced was rather pricey.

I got rid of mine before I got around to doing anything about it.

Wobbliscott mentions a very common problem that certainly drains the battery, the alarm sounder. It is in the near side front wheel arch and gets wet over time and causes all sorts of weird electrical gremlins. Random wipers that cannot be switched off even after pulling the ignition key out are one, as are random radio and drained batteries. I had to replace mine a few years ago after having numerous battery issues and very embarrassing unstoppable wipers! It solved the issues. May be worth investigating.

IIRC there were details on the S-Max Owners Club forum on workarounds.

Ah Highlander has just reminded me a out the blue tooth module, mine failed on my SMAX too; Cant remember if it was around the same time I had the battery draining issue or after but I ended up disconnecting it as a replacement was about £300. I did buy a second hand replacement a few years later for about £50 when they became available on the spares market and that worked fine, but the bluetooth module could also be a suspect part. You have to remove the clove box to access it so just unplug it and see if your battery keeps draining.

Unfortunately just turning off your head unit wont be enough you need to physically unplug the bluetooth module or it will continue to draw power if it has failed.

You know that motor whiring noise you sometimes get roughly 30 seconds after turning the ignition off? I have a theory that sometimes that doesn’t turn off properly. Clicking the ignition on and off again stops it.