Hi,

wonder if anyone can help me? I've gone round the houses so many times and drawn a blank whilst searching despite trying a number of things.

Problem: The aletrnator is overcharging the battery, with a volt meter on the battery as soon as I start up the voiltage keeps rising, slowly but rising and can get to 16-17V!

Discovered: lots of bulbs blew when I returned from a 4 week holiday so after replacing I thought I'd better check the voltage.

History: ~18months ago I had the opposite problem (not charging) and replaced the alternator with an ebay one, at the same time as the dash bulb either blew or the L wire cracked I hooked up a feed to the L terminal of the alternator from the reverse light feed as its ignition switched, no problem at all, everything worked. FYI This feed wire now has a bulb in it just like the dash.

Today: Ignition on -> L feed bulb lights, start car, L bulb feed light goes out (expected as the voltage on the battery and the alternator are the same now -> voltage begins to rise!

Voltage drop checks: +ve and -ve show <0.1V voltage drop and the earth strap/connections have been cleaned and checked just in cae - no issues.

Assumption 1: Voltage reg is dead, local bosch service guys also thought that was likely to give overcharging, so repalced with a new one today, same problem.

Assumption 2: Rotor issue? but is this likley, would welcome anyone's thoughts/experience on this.

Questions: The DFM wire, does this 'just' sense the alternator output or will it trigger the alternator to charge?

Secondary issue: Since this has occured the ABS light keeps coming on when I drive it (I have had to drive it to get the replacement reg etc!) so looks like its doing some damage, so some driving has been done with the alternator dis-connected.

Any ideas or anyone seen this before?

thanks for reading

Im no techie on this subject or anything. But that sounds extremely wrong!.Sounds like a dodgy alternator, i wouldnt drive the car though if it was me. Doesnt sound too good if they ABS light keeps coming on :-S

Not sure about this, but I remember having read somewhere on the forum that the ABS light comes on as an indicator of under/overcharge??? If anyone more experienced can confirm this you'll at least don't have to worry about a second fault.

But probably a good advice not drive till you've sorted the charging problem. Bulbs are comparatively easy and cheap to replace, but when it comes to relays (or ECU :eek: ) it's another matter.

Yup, a bit of googling yesterday semed to suggest the ABS warning is related to the over charging.

The autoelectrician I spoke to today where I got the new reg was mistified and of course it being xmas hols couldn't take a proper look but he didn't exaclt fill me with confidence.

Anyone know of a good autoelectrician in the Guidlford area?

'tis driving me potty...........

its a common thing on the 1.8t engine its normally a replacement alt and wire that goes from the alt to the battery

Thanks mattbeef,

the replacement wire between the alt and the battery makes sense if there is a volatge drop across it as that should tell the reg to keep charging and I think you'd probably get a glow from the warning lamp.

I don't have that problem as far as I can tell it seems sound.

Looks like I need to get both the alternators checked outside of the car using the new reg pack to rule that out - I don't particulary want to shell out for a re-con alternator withoiut being sure its the root cause given I've just spend 42 quid on a new reg.

im sure that i read some where that it would be a new alt.

Ill have a butchers and see what i can find

*Edit*

Have a read of this as i knew it had been mentioned before

http://www.briskoda.net/forums/octavia-i/help-box-top-battery-fuses/87105/2/

well thats some good news, nothing has got as far as melting or overheating, so I've hopefully caught it in time to avoid that.

Update and warning............

so after a lot more thinking and drawing pictures on the office white board none of this made any sense given that the chances of the alternator rotor being dead are pretty slim, likewise the brand new reg pack being duff!

So we went completely back to basics and tried to think of another reason why the voltage reading on the meter kept going up and came to the conclusion that I needed to confirm that the meter was good. It wasn't - doh!

When I started de-bugging this think 3 days ago we did a like for like comparison with a friends ford and verified that his car was fine and mine was definately overcharging. However, since then all this testing has drained the meter battery and low and behold when it was replaced by a nice shiny new 9V cell I get a solid 14.3V charge from the alternator with its new reg pack [dropping to ~13.8 with the works on (blower, rear window heater, lights etc)]. No more stupid 16/17V:)

So to all budding auto electricains out there please check your volt meter! its caused me quite a bit of greif.

Thanks to Mattbeef - pointing me to that post about melting the junction box on the battery really helped work out that perhaps I wasn't still getting overcharging or it would be causing more damage.

Merry Christmas to all and a great 2008.........

PS (I hope I'm not tempting fate by writing this but the cars been running for 20 mins without going above 14.3V so I should be OK)

You will be fine mate just enjoy the car

Good job

Still leaves you with the mystery of the ABS light, though... maybe it needs to be reset?

But that goes beyond my limited knowledge...:P

off topic - why do Skoda/VAG use such random indicator lights? Glow-plug lights for brake light bulbs.... ABS lights for incorrect charge voltage.... do other manufacturers do this, or are Skoda just taking the pi55?

ABS light has gone back to being out,

So all is good and especially as we don't have to use the mini for visitng the in-laws for xmas..... 'tis a proper (i.e. old) min and not exactly fun going up the M40 in it.........

oh dear, took the car on a short 2 mile run to check out the charging (seems fine) but now the ABS light is back on......I think I've been a bit keen to close this out!

Glow-plug lights for brake light bulbs, ABS lights for incorrect charge voltage

In short they don't. The glow plug light is primarily that, as the diesel does not have an engine management light it also has a secondary function as that. It most commonly comes on due to brake light failure but can come on for other reasons as well. The ABS is diagnostics capable and the light will come on for any reason that renders it inoperative, whether it is a dodgy wheel sensor or a power supply problem.

Just to close the issue in case it helps others.

The ABS light was a symptom of a bad connection at the back of the battery, the socket/plug must have gone open when I was checking the battery earthing, so if your ABS warnign lamp triggers at the 12mph mark and you've been doing anything near the battery you might want to check the connections as a first step to correct.