The battery on my MK2 Focus is draining over the course of a few days.  As I'm using my car less often nowadays it means that my car battery can be unusable in about 3-4 days as the voltage drops down into single digits.

I've stuck a current clamp on it and it constantly sits at ~350mA even after being left off for hours.

I've done some googling and it says that this is likely due to a faulty component on the CAN bus which is keeping the bus active and all the attached components powered up.  This can apparently be confirmed because the backlight on the cluster never switches off when the engine is off (mine stays lit all the time).

Unfortunately that makes pulling fuses to locate the culprit difficult as I'd have to wait half an hour after every fuse to know if it made a difference.  I've seen that a common culprit is the internal bluetooth module, but my car doesn't have one so it's not that.

Does anyone know of any common CAN module failures so that I can try pulling the fuses on them first?

Does it have an aftermarket headunit/stereo fitted?

10 minutes ago, WES180 said:

Does it have an aftermarket headunit/stereo fitted?

Sorry I forgot to mention, yes it does, but I've left that disconnected and it's not made a difference. 

I might just leave it disconnected as a sanity check.  If I remove the cable, is it fine to leave it dangling or will I have to re-fit the original stereo so that the cable doesn't fall down?

If you have the original stereo I would try refitting that and see if the problem is still there. There have been numerous posts over the years regarding aftermarket systems causing battery drain.

It may be worth checking your interior lights, including and especially the boot one(s) as the boot switch can become faulty. Got any LEDs? Check them when it's dark to see if they're staying on VERY dimly at all when everything else is off, I've found the interior lights stay on a little while at least when the car is off unless the switches are physically off.

You'll probably notice the cluster light stays on for 30-45mins after the car is off and locked, but that might be another thing to keep tabs on; the ignition barrel can wear and if you have a faulty barrel it can cause the cluster to stay on.

5 hours ago, WireyWhenWet said:

You'll probably notice the cluster light stays on for 30-45mins after the car is off and locked, but that might be another thing to keep tabs on; the ignition barrel can wear and if you have a faulty barrel it can cause the cluster to stay on.

The cluster backlight stays on permanently.  It's never switched off in the 6 years I've owned the car

That's pretty worrying, I've seen mine hit an hour and 30, but if it's on all the time it's either going to be a barrel, or the cluster itself that is draining.. I'd be confident to faff with finding a cluster fuse to pull, knowing if a stuff it it's my own fault and that I could probably source what I need pretty quickly, but of course this isn't my car so I can only suggest what I'd be looking for and warn you to be cautious really.. But to me the root here sound like it's the cluster itself more at face value..

 

This might sound daft too, but the clutch pedal has a switch that when engaged will trip the cluster into thinking the car is about to be turned on, maybe this is something to look at too?

 

Just fyi, if you merely unlock and relock the car without firing it, the cluster stays on a LOT longer than if it was 'driven'- some kind of Ford party trick there :$

A C-max owner had the same problem with the dash display staying on, it was the aftermarket stereo wiring.

If all the original wiring and plugs have not been cut/altered then just pop the original headunit back in to try it before wasting your time looking at other causes. If it's not that then you've only wasted 5 mins.

2 hours ago, WES180 said:

A C-max owner had the same problem with the dash display staying on, it was the aftermarket stereo wiring.

If all the original wiring and plugs have not been cut/altered then just pop the original headunit back in to try it before wasting your time looking at other causes. If it's not that then you've only wasted 5 mins.

Yup, if the Op is going to temporarily disconnect the aftermarket head unit, if there's a CANBUS/steering wheel control box, that also needs to disconnected as that could easily be the reason why the car isn't powering down fully.

1 hour ago, 1979Damian said:

Yup, if the Op is going to temporarily disconnect the aftermarket head unit, if there's a CANBUS/steering wheel control box, that also needs to disconnected as that could easily be the reason why the car isn't powering down fully.

+1 to both of the above! Never twigged about the additional box(es)...

7 hours ago, 1979Damian said:

Yup, if the Op is going to temporarily disconnect the aftermarket head unit, if there's a CANBUS/steering wheel control box, that also needs to disconnected as that could easily be the reason why the car isn't powering down fully.

I had forgotten about the stalk control converter so I pulled that out and left the entire head unit disconnected.  After 30 mins the drain had dropped to 70mA.

It's still pretty high for my liking and the backlight on the cluster still does not switch off.  From what I have read, it should be more along the lines of ~10mA, but it's a definite improvement.  Now I'll just have to figure out why that's happening otherwise I'm without a stereo...