Ford Focus battery warning light on

Car: Ford Focus
Variant: 1.8 TDDI Ghia
Model Year: 1999

Categories: Electrics, ECU, Warnings & Lights

When I start the engine the battery warning light goes off temporarily and then comes back on. I measured the alternator output voltage at the battery and read 16.5V which according to the haynes manual is too high and tells you to change the voltage regulator. This seemed to make sense because I am able sometimes to get the battery light to go off by turning on my lights and heated windscreens which presumably brings the voltage down. I wasn't able to get hold of a new regulator so I replaced the whole alternator, but the fault is still there. I've had a look at the wiring while I was replacing it and couldn't find anything obviously wrong.

Any ideas what else it could be?

Posted: Dec 9, 2011 (13 years ago)

David Brown

Points: 4

If the alternator was charging at 16.5 v it has probably " cooked " battery and wont hold a charge due to cell damage . This will mean any good alternator will be working overtime to try and put power back into battery .Assuming the alternator you fitted has been tested and is o.k .

Posted Dec 9, 2011 (13 years ago)

whittingehame

Points: 38,790

If the battery was cooked from the broken alternator giving out 16.5V I would have thought that would manifest by the car not starting.

I don't fully understand how the charging warning system works but when the engine is running does the battery not become a passive component? How could the battery bring the warning light on?

Posted Dec 12, 2011 (13 years ago)

David Brown

Points: 4

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Ford Focus battery warning light on

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