Hi all, 

Hope someone can shed some light with this issue. 

Recently my 2.0 mk2 focus started lighting the battery light. The battery is fairly recent and the alternator is 1 year old. Voltage does not drop bellow 13 something volta with the engine on. 

This happens mostly while driving in slow traffic or idling for a long time. The light comes one and if I put in neutral the rpm lowers a lot and the engine almost shuts down, but comes back up although at a lower rpm than normal idling (I would say 600 instead of 700).if this happens while already idling you can feel the car vibrate and the rpm drops the same way as explained before. If instate driving at a faster speed without stopping the ligh goes off, although some times it goes off even idling or driving slowly, but that's rare. 

Obd error is p1246. 

 

Thank you for your help. 

Code: P1246, Manufacturer: Ford, Description: Alternator Load Input Failed
Could be sticky alternator brushes.

Sent from my SM-G965F (S9+)

Engine running and everything off I would expect to see 14.6 volts from a voltmeter 👍

1 hour ago, williamweb said:

Engine running and everything off I would expect to see 14.6 volts from a voltmeter 👍

On the obd adapter I never have less than 13.6, even when the light comes on. 

Sounds like the alternator to me.  You have to sort of understand how the batter light works. In short, the voltage from the alternator and battery to the battery light "cancel" each other out. It's only when one side goes lower than the other that the light appears. For example, the batter voltage could be 13.8v, but the alternator is only producing 12.2v, therefore the light comes on.

It's for this reason that sometimes (more specifically on older cars) the battery light only appears very dim, as theres such a small difference in voltage.

On my brothers focus there was a charging problem which was because the one way clutch in the alternator pulley had failed so the pulley was only partially spinning the alternator shaft. It was 1.8tdci, I don’t know if only certain models have that type of pulley.

Check your alternator pulley or auxiliary belt. All symptoms point this way. If alternator brushes are damaged than you would have battery light on all time.