Hi everyone,

For the past few weeks, my car has been very sensitive with it's battery. Repeatedly failing to start after a day or so.

I'm ok with electrics so I decided to diagnose it myself. It has a drain of 170ma.

I started pulling the main fuses in the driver box. I noticed that fuse 3 (F3) instantly stops the whole drain. F3 feeds the internal fusebox. 

So, then I started pulling those fuses.3 fuses cause a small drain of 50ma: F46, F41, F55 (I don't know what these are). If I remove all fuses, there is still a drain of 110ma between F3 and the GEM.

One GEM plug prevents a 20ma drain, another prevents a 40ma drain, and the big green plug (feed plug) prevents a drain of 50ma (or 110ma if all plugs connected). I can't see how 3 different circuits can be damaged, so I'm thinking there must be some sort of short in a MOSFET, regulator or something. I've opened the GEM and it's not really serviceable or diagnosable.

For the past few weeks, I've been disconnecting that green plug, and when I do, the car seems to be fine, however, it's a real pain! The radio resets and the central locking and alarm stops working.

Does anyone know anything else about this problem? Am I right in thinking this is a faulty GEM? I'm thinking of pulling some wires out of the connectors and finding out EXACTLY what the problem is.

Does anyone know anything about this problem? Thanks, Antony...

Those Focususes used to suffer from water ingress into the GEM which could cause a battery drain. Is there any sign of corrosion on any of the pins or connectors? 

14 hours ago, kajeeves said:

Those Focususes used to suffer from water ingress into the GEM which could cause a battery drain. Is there any sign of corrosion on any of the pins or connectors? 

There were signs of corrosion, yes, but only a small amount.After cleaning, there were no traces of any damage.

Ok, and update - a bit of a breakthrough really. The problem is not the GEM!

I incorrectly thought that the GEM was draining, but it was not. It causes a temporary drain of around 170ma until it shuts down, and mine does shut down after around 30-40 minutes. After this time, the drain on the battery becomes around 15ma which is acceptable.

It is not the GEM, but could be one of the following:

F41 - Front passenger door module.

F46 - Instrument cluster supply and OBD.

F55 - Central locking and driver door module.

Ok, an update - the problem is not F55.

F55 causes a further 50ma drain, however, this also shuts down after 30 minutes, like the GEM.

The problem must be to do with:

F41 - Front passenger door module.

F46 - Instrument cluster supply and OBD.

Ok, an update - the problem is not F41.

This also shuts down after some time, like the GEM.

The problem must be to do with F46 - Instrument cluster supply and OBD.

I'll add that fuse in now and see.