I own a focus mk2 1.6 zetec 55 plate. A couple of days ago my battery light came on and the car totaly died on me engine stop and all had to get a new battery to get the car home. I tested the voltage and the battery was 12v engine started drop to around 11 volts turned lights heater on ect and battery drop to 9v. I guessed it was the alternater so change the alternater and its got a new battery what a pain it was getting the new drive belt and air cone belt on. Started the car which it didnt really want to do at first guess it was the cold snow ect and having the battery disconnet for a couple of days. Once i started the engine the battery light was still on odd thing is when i checked it with the mulitmeter the battery was 12v with the engine running it was 14.2 v 14.4 v with all the lights on heater on ect it stayed on 14.2v the voltage didnt drop however the front heated windscreen wouldnt go on and the battery light is still on. So it seems changing the alternator has done somethink hope its not this smart charge system i keep hearing about just seems odd to me that when i put the new alternator in the car is now giving me the correct voltage reading surley if it was a electric or wire promblem changing the alternator wouldnt of changed it form a low reading to a normal reading.

2 hours ago, kory1986 said:

the battery was 12v with the engine running it was 14.2 v 14.4 v with all the lights on heater on ect it stayed on 14.2v the voltage didnt drop however the front heated windscreen wouldnt go on and the battery light is still on.

It sounds like something is still upsetting the ECU.

I see the new battery was drained down to 9v before the alternator was changed. It could be it is still recovering, and the system will settle down in time, when the battery stops drawing high charge current. Or even, a slight possibility, the battery was damaged by that discharge, and will not recover. See how the battery holds up with the engine off. 12.6v is a normal new battery voltage after about 12 hours or more of standby (no charge or drain).

Check Fuse F31 in the engine bay fuse box. This supplies the alternator.

The 2005 Ford "smart charge" was not particularly smart. It used two connections between ECU & alternator, ALT-COM & ALT-MON, to control & monitor the alternator. These are on a 3 way plug (along with the 12v feed from F31) on the alternator. Check this is in ok, with no damaged wires. If this plug is disconnected, or any of its wires are broken, it reverts to a basic alternator regulated voltage output. This will put the warning lamp on, and may disable heavy loads like the screen heater.

The 14v to 14.4v output is about right in either case (engine running).

Other causes include bad earth connections (engine, battery, body), or bad battery +ve connection.

 

Thanks for the reply m8 i will check the fuse tomorrow hopefully with a bit of luck it will be somethink simple like that 

Have you had the car checked for parasitic power drains? (dashcam, black box, glovebox or boot light staying on etc..?)

If the alternator giving power to the battery even with the battery light on will the car still brake down

 

 

21 hours ago, Tdci-Peter said:

 

1 hour ago, kory1986 said:

If the alternator giving power to the battery even with the battery light on will the car still brake down

No.

Providing the alternator maintains its output, then the car will keep going. I suggest getting a cheap (about £5) plug-in (cigar socket) voltmeter from Ebay, so you can keep an eye on the voltage. They can be a bit inaccurate, partly due to voltage drops in the wiring, so cross check with a multimeter at first, but they are good enough to see the difference between charging (13.5v to 14.5v), and discharging (12.5v & below).

Though if your front power socket is recessed like mine, it may be harder to get one that fits.

Also, as you have noticed, some heavy draw items (de-misters) may not work. But basic driving functions should be ok.

Have a check of the 3 way connector on the alternator, make sure it has been re-connected properly.

Just now, Tdci-Peter said:

No.

Providing the alternator maintains its output, then the car will keep going. I suggest getting a cheap (about £5) plug-in (cigar socket) voltmeter from Ebay, so you can keep an eye on the voltage. They can be a bit inaccurate, partly due to voltage drops in the wiring, so cross check with a multimeter at first, but they are good enough to see the difference between charging (13.5v to 14.5v), and discharging (12.5v & below).

Though if your front power socket is recessed like mine, it may be harder to get one that fits.

Also, as you have noticed, some heavy draw items (de-misters) may not work. But basic driving functions should be ok.

Have a check of the 3 way connector on the alternator, make sure it has been re-connected properly.

Will do thanks for your advice really appreciate it i recheck tomorrow after work