Charging control is acting up

Hello!

I need some advice about my T4:
2.5 TDI, ACV engine, 2001.

It's weird again.
During the drive, the charging indicator flickered, then turned on, hesitated for a moment, and now it's constantly lit.

I checked the battery a little while ago, and it's fully charged.
The drive belt is okay.
The Lima is electrically functional and has full power.
Okay, so, if the engine is idling with the lights on, it's still showing just above 14V.
The thin, blue cable from the alternator is properly connected and normally disappears into the wiring harness.

I just removed the alternator; it's a Bosch replacement alternator, 90A.
Although it seems like it hasn't been used much, the brushes and carbon contacts are still in very good condition.

Here's what happens without a bra:
If I only turn on the ignition, the indicator light illuminates with very low brightness, which would likely be difficult to see in bright daylight.
After 5 seconds, a relay switches somewhere in or behind the dashboard, and then the indicator light becomes slightly brighter.
Maybe about half the normal brightness.

Well, what's this now?
the weirdest things always happen with my own cars...

Does anyone have any ideas about what to do next?
without wasting money on pointless things?

Hi G.Steffen!

The charging indicator light MUST be definitely off when the alternator is disconnected.
I would start by checking the (engine) wiring harness for any signs of chafing. Check out the mass.

I once had a similar problem with another vehicle, maybe this will help you understand.
[url]/viewtopic.php?t=25403&highlight=charging light fabia[/url]

Best regards from Munich!

Quote:

The thin, blue cable of the alternator is properly connected, and normally disappears within the wiring harness.

I would first try to determine whether the fault lies with the alternator itself or with the vehicle's electrical system.

The check lamp is located between the DF (Defektanzeige - fault indicator) and B+ (battery positive) terminals. It should illuminate when the engine is running. In its operating state, it should extinguish.

The flickering without the limiter might also be related to the open DF line. When connecting the positive terminal (B+), the indicator should turn off.

Steffen G wrote:

I need some advice about my T4: 2.5 TDI, ACV engine, 2001. Here's what happens without a bra: If I only turn on the ignition, the indicator light illuminates with very low brightness, which would likely be difficult to see in bright daylight. After 5 seconds, a relay switches somewhere in or behind the dashboard, and then the indicator light becomes slightly brighter. Perhaps about half the normal brightness.

Based on the vehicle's year of manufacture, I'm now assuming the traditional wiring of the indicator light (warning light) without a body control module: in that case, when the alternator is connected, no current should flow through the indicator light.
If it's still illuminated, then the cause, in my opinion, can only be due to leakage currents – meaning damp or corroded connectors, or damaged insulation on the excitation cable somewhere between the ignition coil (LKL) and the alternator connector (LiMa). Have fun searching
Alternatively, run a completely new wire from the LKL (likely referring to a specific component or connection point) to the LiMa connector (likely referring to the alternator), and be sure to disconnect the old wire between the two new connection points! This should also solve the problem.

I also wanted to suggest that idea. I wouldn't bother debugging that.

If it happens to be of interest, you can always measure the transition resistance to ground.

Hello everyone!

ulf wrote:

... then no electricity should flow through the indicator when the alternator is connected. ...

+ with the engine/alternator running

Otherwise, electricity MUST flow through the display - regardless of the BNStG regulations or the regulator.

Regarding a cable defect, I would definitely take the time to precisely determine the cause (abrasion/cable break), because if it's the case, a wire rarely breaks on its own .

Best regards from Munich!

DieselBär30x wrote:

Hello everyone! ulf wrote: ... then no electricity should flow through the indicator when the alternator is connected. ... + with the engine/alternator running Otherwise, electricity MUST flow through the display - regardless of the BNStG regulations or the regulator.

Oh, darn, I meant disconnected alternator (as I also mentioned).

Hello!

Thank you for the answers.
I haven't had much time lately.
"But I checked the wiring harness."
It's still in there, neat and tidy, just like the first day.
Nothing was assembled, modified, repaired, or altered.
Therefore, I'm going to take the path of least resistance, which is the one that requires the least amount of work, and I'm going to start by assuming that the wiring harness is okay.
Everything else seems to be working fine.

Autoservice wrote:

The flickering without the limiter might also be related to the open DF line. When connecting B+, the display should turn off...

"That statement is amazing."
because that's really the case.
With the open DF cable, the charging indicator glows faintly.
If I apply 12V board voltage to a small test lamp, it is completely off.
Is there an explanation for that?
It seems like I'll probably have to install a new regulator soon.

Quote:

Is there an explanation for this?

There's almost an explanation for everything. I'm roughly estimating it through induction.

Or rather, capacitive coupling?

I'm sticking with leakage current, because induction and capacitive coupling are high-frequency phenomena that I wouldn't expect to find in such an old vehicle's electrical system.

A leakage current path to ground that causes the glow plug to glow may be "saturated" to such an extent via a test lamp at the DF (distribution box) that the remaining current flowing through the glow plug is no longer sufficient to cause it to glow.
For me, this is a more straightforward explanation than induction or capacitive coupling.

@ Steffen:
Okay, here's the translation:

"If possible, please expand on the LKL, including a possible example." Parallel resistance.
Then measure the resistance of the DF wire (disconnected on the LiMa side) to ground -> it should show an infinite resistance.

Hello!

Today, I installed a new regulator.
That's it.
Everything is working normally again.
Hoping that this will remain the case in the future.

Thank you for your support!

Thank you for the feedback!