Battery light on dash - 02 Polo 1.4

my3cents

Just about home this evening and the battery light went on on the dash.

Got home car will still start battery showing 12.3 Volts engine off and when engine running 11.4 Volts.

Any suggestions as to what to look at first? Are there any well know weaknesses in the alternator or its circuitry? I think the battery is probably OK, put it on charge and its taking a charge OK.

jimgoose

12.3 volts is about 60% charge. And that charging voltage is off the reservation. My gut feeling would be that the battery is dying. How old is it?

my3cents

Battery is about 4 1/2 years old. tbh I'm more than happy to put in a new battery but as its charging away OK (up to 13V atm) I'm not convinced. A new battery is a lot easier than doing anything with the alternator.

jimgoose

my3cents wrote: »

Battery is about 4 1/2 years old. tbh I'm more than happy to put in a new battery but as its charging away OK (up to 13V atm) I'm not convinced. A new battery is a lot easier than doing anything with the alternator.

Your reasoning is sound enough. It would be interesting if possible to see what the car's charging voltage is like with a known good battery, though.

my3cents

Just back in after walking the dogs and battery is still charging and its at 13.9V. I'll leave it on all night and see what readings I get when I start the engine in the morning.

Irish Steve

If the battery warning light is on, or comes on when driving, that's usually an indication of a possible alternator issue, the two most likely issues are a lack of drive from the belt, or the regulator in the alternator has failed, which may be an issue with the brushes in the alternator. IF the belt has failed, on a lot of cars, it also drives the water pump, and maybe the cooling fan, so a failure will usually also lead to the engine overheating pretty soon afterwards, which is not good, so check that the belt is still there and that the alternator is turning. If you were nearly home, given the temperatures today, you may have got home before the temperature rise became critical if it is indeed a drive belt issue. If the belt is still there and the alternator is turning, and the warning light is still on, then the most likely issue is that there has been some sort of failure with the alternator.

The battery has done well to get to that age, and with the way the temperatures have been this last few days, if it is on the way out, the lower temps will expose that weakness, but a failing battery doesn't normally lead to the warning light coming on, the usual symptom will be a reluctance to start in the mornings.

my3cents

No nothing quite as obvious as a broken drive belt - that was replaced when I did the timing belt back in the summer along with the water pump.

The alternator is turning as it should do and wasn't overheated when I switched the engine off.

I posted here just in case there was some well know n component that failed on these. First thing I'll do in the morning is look for damaged or broken wiring because when the battery warning light first came on most of the other dashboard electrics failed, main lights stayed on but radio wouldn't come on, odometer went off, temp and petrol gauge showed zero but came back again after a couple of minutes driving? All fuses including the ones on the battery are OK.

Second up is identify whose alternator it is then I'll look for more info on the specific alternator.

brembo26

Have had to change a good few alternators in golfs and polo's of that vintage.

Best way to check the alternator is to check its output under load so make sure your lights are on and have the interior fan on as well. A good alternator should ideally be providing 14 volts or there abouts.

my3cents

brembo26 wrote: »

Have had to change a good few alternators in golfs and polo's of that vintage.

Best way to check the alternator is to check its output under load so make sure your lights are on and have the interior fan on as well. A good alternator should ideally be providing 14 volts or there abouts.

I'll check that again tomorrow, with the fan on full but no head lamps it was only showing 11.4V across the battery.

brembo26

Thats not enough to power the accessories and charge the battery at the same time. Looks like a new or reconditioned alternator is in order i'm afraid.

my3cents

Much what I expected but take a look in case its anything really dumb first.

alta stare

Battery light on dash points to an alternator issue. Usually around 90 quid to have reconditioned.

my3cents

Any ideas where to get a replacement alternator or to get one reconditioned?

Irish Steve

Depends on where you are in the country.

Most motor factors and independent garages will be able to get one quite quickly, if it's not on the shelf, if it's desperately urgent, are you near a Halfords, though they can be expensive.

You could get a used unit from a scrap vehicle, but the life of such a unit is unpredictable, or you could take your unit to a reconditioning company and get an exchange unit.

Without knowing where you are, it's hard to give precise advice

my3cents

I'm down near Waterford. I think there is a guy in Dungarvan that does that sort of work, must find out where he works out of. Just off out now for a quick look underneath at the wiring then to take the old unit off to see what make it is and if I can do anything easy myself like replace the brushes.

my3cents

Have the alternator here on the desk and looking for a spare. The part is this but probably won't get it until Wednesday. I'd hoped to get one a bit quicker, one local motor factor could only quote me for what I guess are cheap copies and I'm still waiting for the other to get back to me? Deise motor factors in Waterford sounded good but then wanted a cash deposit before they would get the part in and I don't really want to do a 70 mile round trip just to give them a deposit.

Edit> After being offered another brand I'd never heard of by the local motor factors I went with the genuine Bosch one in the mister auto link above approx €245 but will probably have to wait a week for it to arrive.

alta stare

my3cents wrote: »

I'm down near Waterford. I think there is a guy in Dungarvan that does that sort of work, must find out where he works out of. Just off out now for a quick look underneath at the wiring then to take the old unit off to see what make it is and if I can do anything easy myself like replace the brushes.

Dickie Mcnamara down in waterside in the city centre does em. Usually has it done next day.

my3cents

Just to follow up, fitted identical new Bosch alternator and its working fine. Used Mister-auto.ie and new part took a week to arrive (expect that from Belgium) and cost about €180.

brembo26

Good to hear! Did you have to send your old one back?

my3cents

brembo26 wrote: »

Good to hear! Did you have to send your old one back?

Still have it here, will send it back on Monday. Price was something like €250 with €70 credited back when the old one is returned.

tbh I don't really know if I have a reconditioned unit or a new one, it looks new and came in a new box but had a genuine Bosch eXchange label attached to the unit so I guess its a rebuilt reconditioned unit.

Now I just have to sort out the seat belt light on the dash (see my other thread) and of course nothing is easy as the end of the bonnet cable broke so I had to break into the bonnet to do the job.