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Focus Mk 2, 1.6 Petrol - Battery Warning Light


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I've got a version of the battery warning light problem that I've seen mentioned in various places. This started two days ago. I checked the battery and the "magic eye" showed more than a hint of red so I bought a new (silver calcium) battery. I fitted the new battery today but the problem persists.

The symptoms are:

Battery warning light is on all the time.

Front windscreen de-icer won't work.

The car starts and behaves fine and has been on a 100 mile plus journey with the battery warning light on and using the old battery with lights and heater/blower on constantly.

No logged faults (I've got a bluetooth OBD2 adapter which is where the voltage/rpm readings below come from via Torque on my phone).

With the key in second position and engine off and nothing (heater, lights etc.) on the voltage reads 12.5 dropped to 12.3 within a minute or so.

Turn headlights on, voltage dropped to 11.9

Blower and lights on voltage dropped to 11.7

Car at idle (910-930 revs), voltage constantly changing between 13.4 and 13.5

Headlights on, voltage went down to 13.2 then jumping between 13.4 and 13.5

Headlights and blower, same as headlights only.

When I hold the revs at approx. 2000 rpm, no electrics on, the voltage jumps between 13.5 and 13.6

Switch the headlights on, voltage dropped to 13.2 then jumps between 13.5 and 13.6

Headlights and blower on, same as immediately above.

My first question is, is the OBD adapter giving me the voltage info that I need or do I have to use a multimeter (which I don't have!)?

Next, does this sound like the alternator is dying? I don't know how old it is but, from a quick visual inspection, it doesn't look that old.

There was a lot of wiring around/connected to the alternator so I didn't feel confident enough to check whether there were any wiring issues without being pointed in the right direction of likely culprits. I couldn't see any problems but everything was covered in rubber "boots"/sheathing.

Finally, could the old, almost duff, battery have caused problems which blew the fuse for the front windscreen? If so, which fuse is it? Is it under the bonnet or in the passenger foot well? (Wouldn't it be nice if the solution was that simple?!)

Many thanks, in advance, for any info./suggestions.

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First impressions are it's the alternator. I'd expect about 14.4V at anything much above idle. I seem to remember there was an issue with the alternator loom on early models and a Ford technical bulletin about it. The fix required adding an additional wire I think. Hopefully one of the gurus will soon be along to clarify the issue.

It seems more likely that an alternator problem has caused the duff battery.

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