04 2.0d Charging Circuit - EricMears
My C-max is behaving rather strangely.

The alternator warning light comes on when you switch the ignition on & goes off when the engine is running (i.e. just what it should do) but checking it more thoroughly with a voltmete in the cigar socket, the battery voltage gradually drops over several days and (unlike my other car & every other one I?ve tested) doesn?t shoot up to 14V whilst the alternator is running. I?m thinking ?alternator relay? but perhaps there are other possibilities (hopefully even a fallen off wire).

Exactly the same thing happened back in November but for no apparent reason it righted itsellf after a couple of days.

I've seen an item in another forum about 'slipper bearings' but my alternator does appear to be turning (& in any case if it was stopped , shouldn't the warning light come on ?). Does anyone have any ideas ?

04 2.0d Charging Circuit - DP
These have 'intelligent' alternators which only charge the battery when needed. I know this because a friend bought one of the very first ones of these brand new back in 2003, and had repeated instances of flat batteries in the first few weeks, which took two software updates on the charging system to resolve. In fact, the whole car took several months of software patches before it became useable, but it's been great ever since.

Is the battery actually going flat?

04 2.0d Charging Circuit - EricMears
Thanks for your input.

When this happened a few weeks ago I was in two minds whether it was alternator or battery but after a couple of days uncertainty (& several overnight charges) the system seemed to right itself and was indeed chucking out 14v when running. It was of course the battery then (other evidence as well) so that's now been replaced (& yes, new one has got a 'silver' label on it). New battery hasn't actually gone 'flat' yet - but only because I won't let it; I'm sure it would if I just ploughed on.

After 2hrs charge I've just taken it for another run. There was a hint that voltage was higher with engine racing than ticking over but it definitely dropped as lights were switched on. Now charging overnight & will take it for another run tomorrow.

I'm inclined to suspect the 'smart charge' system too but am not sure what to replace to cure that. I presume there's an alternator relay somewhere in one of the fuse boxes but the owners handbook is less than helpful on which of the anonymous black boxes it will be.

Not directly connected to this query but does anyone have a list of which fuse does what ? Handbook claims there should be a list in box but I'm blowed if I can agree that it's any help at all.

I've owned the car since new and until last November had never had any bother with it. I have actually replaced it but it's now being driven by my son.



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