Charging indicator light goes out briefly after engine start

Hello everyone!

Since this afternoon, I've been experiencing a strange phenomenon with my A6 TDI V6, manufactured in 1998. When I start the engine, the charging indicator light goes out and then comes back on after about 0.5 seconds. It then stays on as long as the engine speed is above approximately 2500 RPM. After that, it doesn't come back on, even at idle or under load. When the indicator light is on, the voltmeter only shows slightly above 12V. As soon as the indicator light goes out, the voltage returns to the usual 14V.
Immediately after starting, you can hear a relay click at the same moment the light goes out. When the light comes back on, it clicks again. I've managed to determine that it's likely the so-called 'generator switch relay.' Whatever that might be necessary for!
Does anyone have any idea what might be causing this? It started suddenly, from one day to the next. I've never had any problems with the inverter or the regulator before. When it starts running, it seems like everything is okay... until the next time you try to start it...

Thank you for your help!

DENNIS

Hi!
Unfortunately, the term "generator interlock relay" means absolutely nothing to me. Maybe someone else can provide some information. However, the remaining description clearly indicates a defect in the pre-excitation system of the Lima.
However, based on the speed you mentioned, the residual magnetism seems sufficient to generate the required voltage in the stator windings. Once this threshold is exceeded, the Lima system becomes "active" internally and independently through the controller.
The strange thing is that the warning light illuminates when the ignition is turned on. That, in turn, is actually an indication of a healthy initial excitation and a closed initial excitation circuit.

Sincerely,
Sure, here is the translation of the text from German to English:

"Dirk"

That sounds more like a problem with the afterglow function!

The afterglow consumes so much power that the battery can no longer be charged!

The afterglow will be stopped at speeds above 2500 RPM!

That still doesn't explain why!

Regards,

Manuel.

Hi!
@Manuel Thomas:
Since the preheating system is generally protected by fuses, it is extremely unlikely that the power consumption of the heating elements would increase to the point where the Lima system fails. I believe the same applies to the coolant heating elements, if that's what you were referring to. The fuses would trip before that could happen. Furthermore, the control light would likely appear much brighter because the potential difference would be lower than in a non-excited alternator.

Best regards,
Sure, here is the translation of the text from German to English:

"Dirk"

Hello Manuel!

This might not be related to afterglow, as it also happens when I turn off the engine while it's still warm and then start it again a few minutes later. It should have been completely cool and stopped glowing a long time ago!

DENNIS



That sounds more like a defect in the afterglow process!

The afterglow consumes so much power that the battery can no longer be charged!

The afterglow will be stopped at speeds above 2500 RPM!

That still doesn't explain why!

Regards,

Manuel

Yes, it will glow every time the engine starts, whether it's cold or warm.

This reduces engine noise, improves idling, and lowers emissions!


The glow plugs in the water circuit are controlled via the DF terminal to prevent excessive load. Depending on the available capacity, 1, 2, or 3 glow plugs are operated. Not with standard spark plugs.

Regards,

Manuel.

Hmmm... I'm not entirely sure, but I'm going to try pulling the glow plug relay tomorrow. Then it shouldn't glow even when the engine is warm.
Otherwise, I suspect the voltage regulator of the alternator might be the problem. This seems to be somehow related to this peculiar 'generator switchover relay.'

DENNIS


Yes, it will glow after every engine start, whether the engine is cold or warm.

This reduces engine noise, improves idling, and lowers emissions!

Regards,

Manuel

hi
I think Brezelmann is on the right track; the problem might be related to pre-excitation. Does the car only have a diode for charging control? If so, there must be a parallel resistor somewhere through which a larger current flows than through the diode, which is necessary for pre-excitation. You should check that resistor.
Good luck.

Hello Gerrit!

Interestingly, there was no sign of the problem today. After the cold start, the light (I'm not sure if it's a bulb or an LED) went out and stayed off. Even during the afterglow phase (about 1 minute), it remained off, although the voltage indicator showed only 12V at idle. When starting later without preheating, it also turned off as usual and didn't come back on.
Regarding the afterglow: I think Manuel is wrong. Because after the engine has warmed up and started, no electricity is sent to the glow plugs.

DENNIS


hi
I think Brezelmann is on the right track; the problem might be related to pre-excitation. Does the car only have a diode for charging control? If so, there must be a parallel resistor somewhere through which a larger current flows than through the diode, which is necessary for pre-excitation. You should check that resistor.
Good luck.

hello
Let's wait and see, I think your problem will come back. You probably won't find a "Heinzelmännchen" (a mythical creature often blamed for missing objects) in your case either. By the way, it might make sense because a poorly connected connection on a circuit board (just clipped in) can sometimes conduct electricity well and sometimes not. You can let me know if I'm right.
CU
Gerrit.

Hello Gerrit!

The problem occurred consistently on Saturdays, but it has since disappeared. It hasn't happened again even once. Everything is very, very strange.
As far as I'm concerned, it shouldn't happen again.

Hi,

I once experienced a similar phenomenon with an Audi 80. It turned out to be caused by a broken wire for the excitation of the alternator (terminal D+). The alternator only started charging after a specific engine speed was exceeded once (~2000 RPM). However, during the cable break, the charging indicator did not light up continuously, and the voltmeter also remained at approximately 12 volts until the charging process began.

Regards,
Olli.

Hello everyone!

Last Friday, the charging indicator light came on during the drive and wouldn't turn off. Even when trying to start the car on Saturday, it wouldn't work. It briefly turns on and then immediately turns off again. According to the voltage meter, no power is coming from the alternator.
The timing couldn't have been worse. Friday evening, 7 PM... and on Sunday, I was supposed to drive 550 km to Hamburg *sigh*.
After returning from Hamburg on Wednesday – my AFB is definitely a much smoother ride than the 1Z *lol* – I went to the Bosch service center today.
It started well with the phrases 'No problem' and 'It's not that bad.' We agreed to check the alternator and, if necessary... Replacement of the regulator, and in the worst case, the alternator.
Then it was time for the prices... I wish I had just stayed in bed. LiMa, approximately 460 euros for installation, 2.5 hours (according to the price list).
Whoever designed this bra so that it takes 2.5 hours to change should spend the rest of their life only taking these things apart and putting them back together .
After 5 hours, the nice man from Bosch service called me and told me that they had the alternator, but there was nothing more they could do... it looked very bad.
So, unfortunately, a 'new' one has to be installed. And by the way, he also mentioned that 2.5 hours is definitely not enough time, and that I should expect to have to put in some extra work...

I'm curious to see how much I'll end up having to pay... but I'm bracing myself for around 800 euros... and that's for a bra *sigh*.

Okay, here's the translation:

'Let's try a different question... if they've listed 2.5 hours for the exchange in a list, shouldn't they be able to complete it within that time?' Or do I have to pay extra if the installer is incompetent?

DENNIS

Hello everyone!

If it's still of interest...
I was able to pick up my car from the Bosch service on Friday. They wanted to charge me for a full 4 hours of labor! I reminded them again about the estimated time of 2.5 hours listed, and I also received information from Audi that it also takes 2.5 hours for the replacement there... and sure enough, the 4 hours were reduced to only 3 hours . They take those 30 minutes to check the old alternator to see if anything can be salvaged. I think that's fine so far.
But the unbelievable part comes at the end...
The replacement cost of the timing chain tensioner (LiMa) is MORE EXPENSIVE at Bosch than it is at Audi! You would think that getting a part directly from the manufacturer would be cheaper... 'Nonsense... if Audi had worked according to their estimate, the repair would have even been 10 euros CHEAPER than with Bosch '.
Well... maybe it's not always so wrong to ask the 'friendly' person for a favor .

Regards,
DENNIS

... and I also received information from Audi that it also takes 2.5 hours for the replacement there...

However, it's usually assumed that all the necessary specialized tools are available and that the mechanic has already performed this type of work before.

It's quite generous of your colleagues, as you (as far as I know) don't have any entitlement to those (Audi-specific) time slots.

... and I also received information from Audi that it also takes 2.5 hours for the replacement there...

However, it's usually assumed that all the necessary specialized tools are available and that the mechanic has already performed this type of work before.

It's quite generous of your BDs, considering that you (as far as I know) don't have any entitlement to the (Audi-specific) times.

Hello Martin!

I don't think that's particularly generous. When I inquired, the representative said that Bosch has a standard time of 2.5 hours for this type of repair. If someone else does it, and they don't have the knowledge or the right tools, shouldn't that be their responsibility, not mine?

DENNIS