Skoda Fabia 6Y: Charging indicator light not illuminating (SOLVED)

Hello everyone!

I just received the AI (part number: 6Y0 920 870 D) from the above-mentioned source. The vehicle was disassembled to check if the faulty charging indicator light was a light bulb and, if so, to replace it.
Unfortunately, it appears to be an LED.

With VCDS, the "charging control light" function is not included in the actuator diagnostics, so I couldn't test it separately.

There is _no_ voltage on the blue cable leading to the generator (disconnected plug!). However, if you connect a light from +D/L to B+, it lights up and then goes out after the engine starts. Charging regulator. O.

Since I don't have an electrical wiring diagram, I need your help with the "+D" or "L" wire.
Does this data go directly from the generator to the AI? If so, which pin on the multi-plug can I use to measure this?

Thank you very much in advance for the quick help!! (waiting for it )

Greetings from Munich!

Should the charging indicator light not illuminate when the ignition is turned on, just like all the other indicator lights?

Hello Voodol!

...well, what do you think the reason is that I expanded the AI?

Best regards from Munich!

Okay, now I understand the problem .

Have you ever externally powered the LED?
Passage checked?

If you use a multimeter and connect it with the correct polarity, it should glow faintly due to the test current.

DieselBär30x wrote:

... Since I unfortunately don't have an electrical wiring or circuit diagram, I need your help with the "+D" or "L" wire: Does this data go directly from the generator to the AI? If so, which pin on the multi-plug can I use to measure this? ...

voodoo wrote:

... Have you ever externally powered the LED? Passage checked? ...

Thank you for the help .

Just received a private message from "auditom":

auditom wrote:

Hello Dieselbear, Take a look below, near the starter motor. There are several cables plugged in, including the cable for the charging control. There are two cables in the connector. Try pulling on all the cables, and then unplugging and replugging them. There's a 99% chance the problem is located there. Best regards from Erding. Tom. PS I couldn't write in the forum because I'm brand new and just signed up.

Thanks, Tom!

As I replied via private message, our sales representative has returned home with the Fabia. I will check the location at the earliest opportunity and report back here.

Best regards from Munich!

DieselBär30x wrote:

Since I unfortunately don't have a wiring diagram or circuit diagram, I need your help with the "+D" or "L" wire. Does this data go directly from the generator to the AI? If so, which pin on the multi-pin connector can I use to measure this?

If the circuit is identical to 9N or 6L, the alternator pre-excitation comes from the BN control unit, which also remotely controls the charging LED (presumably via CAN).

ulf wrote:

If the circuit is identical to either 9N or 6L, the alternator pre-excitation comes from the BN control unit, which also remotely controls the charging LED (presumably via CAN).

That's exactly how it is, Ulf.

Hi Ulf!

Thank you for the information!
The GTI-TDI representative had already explained something similar to me over the phone regarding this case.
Subsequently, I tried to extract relevant information from the German Federal Network Agency's (Bundesnetzagentur) database that might refer to the LiMa project, but unfortunately, I found nothing. The generator load is described in section 12 of the German Renewable Energy Sources Act (EEG).
I am also surprised that the BNStG (presumably a diagnostic log) does not record an error related to "unlikely signal from terminal D+", and that the battery indicator light is illuminated on the KI (likely a control unit).

According to the basic circuit of a LiMa regulator, a "lamp" should be connected between terminal 15 and... A D+ connection, which represents an Ohmic load, must be present in order to enable its control.
With a properly connected plug on the generator, there should be approximately 12V on the cable side – however, the measurement showed only 200mV.
Surprisingly, the system still works. While there are constant voltage fluctuations between approximately 14.4V and 14.6V, and the "generator load" reading is inaccurate (40% with all consumers OFF, 60% with all consumers ON).
Immediately after starting the engine, the alternator is not working. The on-board voltage remains at approximately 12.2V, according to [source/instrument]. The generator only starts working after a brief increase in engine speed, and only then does it produce power.
Can someone confirm that the 12V should be present at the "+D" input of the alternator regulator, both when the BNStG (battery control unit) is active and the ignition is on (without the engine running)?

Thank you again!

Best regards from Munich!

DieselBär30x wrote:

According to the basic circuit of a LiMa regulator, a "lamp" should be placed between terminal 15 and... D+ - i.e., an ohmic load - must be connected in order to enable its regulation.

No: the regulation itself works even without external power, once the alternator ("LiMa") has "started," meaning it is generating its own voltage.

Quote:

With the connector plugged into the generator, there should be approximately 12V on the cable side - the measurement was 200mV.

Using a high-impedance DVM? Or could those 0.2V at a short circuit to ground have supplied a few milliamperes of current? If so, I would suspect a faulty output of the BN control unit.

Quote:

Surprisingly, the regulation still works.

Although there are constant voltage fluctuations between approximately 14.4V and 14.6V, the alternators in our TDIs (9N and 6L) have a soft load-up response to smooth out any jolts in the belt drive when strong consumers are switched on. Translation: Cause: A brief voltage drop, for example, when turning on a fully decorated Christmas tree.

Quote:

as well as the MWB "generator load" reading is incorrect (all consumers OFF: 40%; all consumers ON: 60%).

That is probably quite strange .

Quote:

Immediately after starting, the alternator does not function. The onboard voltage remains at approximately 12.2V according to. VCDS, and only after a brief increase in speed does the generator start working.

This is normal: small residual magnetization in the rotor is sufficient to allow the alternator to "start" at the appropriate speed, even without external excitation, as mentioned above.

Quote:

Can someone confirm that the 12V should also be present at the LiMa regulator input "+D" via the BNStG (Battery Monitoring and Signaling System) and ignition ON (without the engine running)?

IMO, it should be that way, as far as I remember from other forums (with similar problems).

Hi Ulf, and thanks for your reply!

That explains a lot .

200mV measured with a DMM (Fluke 87), internal resistance 20 MΩ. Current versus...? I didn't measure the mass because, as far as I understand, there's nothing to measure at 200mV.

The voltage drops were measured with no loads connected and without turning any devices on or off. According to the measurements, the voltage dropped significantly with a large number of devices connected. VCDS reading below 13.7V - however, the voltage fluctuations (+/- 0.2V) remained.

The car is expected to be back here next week. Okay, I'll start by following Tom's suggestion and looking for the power outage.
Does anyone have a copy of the BNStG? Can you provide me with a wiring diagram for "D+"?

Best regards from Munich!

DieselBär30x wrote:

The voltage fluctuations were measured with the engine idling, without any loads connected, and without turning any loads on or off. According to VCDS, the voltage dropped below 13.7V with as many loads as possible connected; however, the voltage fluctuations (+/- 0.2V) remained.

Was everything read from VCDS? Then throw the data in the trash .
The charging voltage is best measured directly at the battery using an analog multimeter (to visually smooth out the pulsations from the rectification process).

Quote:

Does anyone have a wiring diagram for the BNStG (Body Control Module) or the "D+" lead?

Specifically, on the 6L model, the (blue) cable runs through 2 connectors (as far as I know, in the area of the starter and in the splash guard) to pin 9 of the 18-pin BN-StG connector "XS4". The BN-StG is located above the clutch pedal.

Ulf, thank you again!

I will let you know as soon as I have the Fabia back (and can actually work on it *g*).
The tip from Pin 9(1 BNStG was very, very helpful!

Best regards from Munich!

I've observed the same phenomenon in a Polo 9N. The indicator LED is not working.

'New battery. Wiring harness in good condition. New engine control unit. New body control module.' LED in the ICU is OK.


Test a new/different AI before you spend €300 (+/- several €) on a BNSG.

Hey Mulle!

As I mentioned, I haven't had much time to work on it yet.

"I'll start by measuring the 'D+' line up to the BNStG, and if that's okay..." B. Then, for reasons of profitability, it will be left as is.
The Fabia (with automatic transmission) has already covered over 330,000 km, runs perfectly, and... well, especially with a woman behind the wheel, it's a miracle! *laugh*

Mulle, if you happen to find the error in the Polo, please post it here!!! (even if it's years later *g*)
Regarding the (perhaps not so) controversial topic, there's apparently an issue with the wiring harness collecting water and corroding. The VAG solution: cut it open! ...Alternatively, replace it if there are serious defects. Furthermore, in addition to the "charging light" warning, there's also been a failure of the electric power steering pump, which our sales representative has sporadically reported during cold starts a few months ago. "Using VCDS, all error memory locations were clear, the power steering control unit was functioning properly, and the "Servo" error has not reappeared since (after I told her to take her hands off the steering wheel when starting the car!)."
The aforementioned action was apparently not performed on this vehicle, as there is no action sticker attached to the A or B pillar on the driver's side. The ship's logbook is also missing. (=WeiBär... )

I will report back when I have the WunderFabia in my hands again .

Best regards from Munich!

Furthermore, in addition to the complaint of a 'charging indicator light,' there was a failure of the electrical. Power steering pump issue, which our sales representative had already sporadically reported a few months ago during the morning cold start.

This one goes a step further. You start driving, and then it completely shuts off. The battery is DEAD. It is also NEW, for example.

Now you


Regarding that:

When the battery is charged, it lasts for a few days. Then, it turns off and is empty. Without warning, unexpectedly.

Food for thought: Engine start - charging voltage approximately 10...11V - accelerate - the voltage drops from approximately 2000 RPM to around 13.8V and then remains at that level. All connections and wiring have been checked. No errors to find.

Funny: Turn the ignition on, and after 2...3 seconds, ALL the lights go out. AI looks like a key in a pocket .