Audi 8l S3 amk charging issue

[Xploding_S3]

Hi Guys

If this thread or issue was covered before , can you please direct me to it.

A breakdown to my issue,

Symptoms and issues :
Battery light is on for a few months.
Car starts and runs well, so I ignored it,
A month back , I started the car and it drained the battery,

I sent the battery for charging , refitted it , started the car and found the car was running on the battery.
Did some test - found no charge was getting to the battery , I traced it to the fuse, no issues with the fuse(Fuse box on battery for alternator), I took out the fuse , cleaned(white stuff on it), fitted it and now i was getting charge over it.

More testes:
took of the alternator for testing , ran it on the bench and got a reading of 14.2v, all seemed fine,
fitted it back to the car.
Cold start - reading at the battery was 14.08v at the alternator - Battery 14v.
car warms up , load increases and this reading drops - Alternator +- 13.7v and battery 13.8v.
With the lights on im getting 13.6v at the alternator.
Belt on the car is less then a year old as well, got it after buying a new battery.

Battery light still remains on and the battery is less then a year old, and has been tested a month ago,

I found i was losing 0.1v when doing drop test so i added a new 4g cable from the alternator to the battery fuse box, 4g cable from the fuse box to the positive post,
4g cable from the negative post to the gearbox , 4g from the gearbox to the head.
small improvements when the car is warm, less voltage drop.

however im still getting the battery light and im still finding readings around 13.6v to 13.8v.

Areas i need to look at - regulator , ecu signal to the alternator or alternator clutch?
help please,
Im worried if i change the alternator then it could be the ecu,
so if you know how to test that signal, that will help.

alternator is a bosch 120a - fuse on the car is a 150a

 

[desertstorm]

The light on the dash is controlled by the indicator wire that comes from the regulator on the back of the alternator. The voltage readings you are seeing are similar to what I get on my TT and there isn't anything wrong with that.
The ECU has nothing to do with the alternator. Changing the control box on the alternator may resolve your issue, you may have a diode gone duff in the bridge on the alternator though so the best idea would be too replace the alternator.
The alternator produces 3 phase AC and this is rectified by a 6 diode full wave bridge. If one of the diodes in the bridge fails you will still see high voltage off load but there will be a lot of ripple in it on load. Depending on the meter you are using you may not see this ripple though.
How many miles has the car covered ?.
You can buy a cheap second hand alternator for not a lot of money
https://www.ebay.co.uk/itm/Volkswag...Alternator-028-903-028-E-120amp/283340015538?
New ones from £100 up depending on what make you want.
https://www.ebay.co.uk/itm/AUDI-S3-...E-028903030A-038903024F-Quality/332953619606?
http://assets.fluke.com/appnotes/automotive/beatbook.pdf

 

[Xploding_S3]

the car has covered over 200 000km +,
thank you for the feedback ,

Why i did state the ecu , i assumed the ecu sent a signal to the regulator when the car is under load,
if im wrong then thats going to clear alot,
It would mean , replace the alternator ,

 

[hendo#1]

There is a voltage regulator and a set of brushes on the back of the alternator, all comes in a 1 piece unit.

Cheap and easy to replace, thats the first thing I’d be doing.

I replaced mine last year after my battery light came on and the battery wasnt charging.

 

[Xploding_S3]

I did think of replacing the regulator , but i wanted to trace/trouble shoot to that item, anyone know how to?

 

[Xploding_S3]

i did the above test and got no reaction from my alternator output when load was put onto it, could this be the result im looking for to replace the regulator?

 

[desertstorm]

The ECU doesn't control the alternator. The alternator provides a signal to the ECU so the ECU knows how much load is on the alternator .
On newer cards the alternator could be controlled by the body control electronics so it only charges on overrun and things like that but it's not that fancy on the older cars.

 

[Xploding_S3]

thanks for confirmation , i needed to know this,i will strip an replace my regulator as its a simple option,and makes sense to try it first

 

[Xploding_S3]

update : Regulator has been changed and a big improvement.
Problem is still not solved.
Issue : Battery light is still on - Voltage reading is 14.1v and holds even under load,
Lowest reading with lights and fans on was 14.01v.

My battery light is still on as im assuming that the alternator needs to push out more than 14.1v - expected 14.2v - 14.4v.

before I replace the alternator , im going to check and see if i need to replace the tensionor pulley,

 

[Xploding_S3]

I pulled fault codes:
18010 power supply terminal P1602 -35 -10
any idea about this?