Audi A4: Starting Problems Below 5°C?

Hello everyone,

Maybe one of you knows the solution.

Below 5 degrees Celsius, all the gauges twitch for a few seconds after starting.
The lighting also flickers excessively. It should also be noted that the lighting for the heated seats flickers as well. The longer the problem persists, the colder it is. Everything else functions normally.
My A4 is from the year 2000.

Unfortunately, I don't have a wiring diagram for the AI.

What I have already checked.
- Large cable on the left side of the footwell.
- VAG-COM shows no errors, but...

Measurement block 3 is displaying an invalid temperature (see photo).

Thank you in advance for any tips or schematics.

Rainer.

Hello everyone,

I've done some more searching.
All switch lights, including the air vent lights and the radio, are flickering. This happens for about 5 minutes at these temperatures.

I checked it again. The voltage is stable, but the 12V is dropping.

Today, I'm going to try feeding the 12V power from the back, just for testing purposes.


Does anyone have any other ideas or a circuit diagram?



Okay, here's the translation:

Thank you.
Rainer.

With which version of VC was the recording made?
and which control unit (part number) was used?

For A4 models, it's usually the potentiometers for the lighting control that are the problem, often.
Is it enough to just quickly rotate it back and forth a few times?

vagtuning wrote:

With the A4, it's usually the potentiometers for the lighting control, often. Does it help to quickly rotate it several times from one position to the next?

I know what you mean, but I haven't seen the pointers jump yet because of that.

Hi,

Didn't older Audis have a voltage regulator in the instrument cluster, where the solder joints would occasionally break? This would cause the needles to jump erratically.

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

"Micha"

Mephisto wrote:

Didn't the old Audis have a voltage regulator in the instrument cluster, whose solder joints would occasionally break?

This would cause the needles to jump.
Yeah, that's exactly what the old Audis were like.

However, I wouldn't classify the Audi in the same category as those where this issue might still be a problem.

Mephisto wrote:

My A4 is from 2000.

Hello datsun/Rainer,

That sounds more like a general power supply or fuse issue (excluding occasional short circuits or high current draw from the infotainment system).

What are you trying to do with the externally supplied 12 volts?

Do you have the possibility of using an oscilloscope (a DVM is usually too slow) to check the 12 volts while you are 'messing around' with the fuses?

Is there a single fuse that powers everything? If so, I could measure the current flowing through that fuse to differentiate between a short circuit and a loose connection.

Do you have the wiring diagram (power supply from the control unit and ventilation nozzle)? Otherwise, I can 'consult' my documents.

Best regards,
Kassen Oldewurtel.

Hello everyone, first of all, thank you for your sympathy.

- I would rule out the issue with the oxidized potentiometer, because I don't have brightness control (or haven't found it yet in the AI).


'When I feed power in reverse, the lights get a little brighter. But the AI still flickers. I need to do some power measurements. Currently, the wire gauge is a bit too small (about 0.2 mm²), which could explain why the effect is so weak.'

-Also, the mileage and daily kilometers have not been reset, but the overall mileage is okay.


- 'Fumbling around' hasn't shown any effect so far.

I currently do not have access to a scope.

- All screw terminals on relay base X75.30 are secure.

A circuit diagram is needed so that it can be determined where the problem originates.


Tomorrow morning, we'll continue, and the temperature will be ideal.

Best regards, Rainer.

Hello Rainer,

Unfortunately, your signature does not contain the important information about the vehicle (specifically, the exact vehicle type/year/frame number).

Please send the data using the part number . I will then check to see if I have any corresponding wiring diagrams }.

Best regards, Kassen.

Hi,

Quote:

Yes, that's exactly what the old Audis had.

When it comes to newer devices, powering indicator instruments with "fluctuating" voltage is never a good idea. The voltage must be stabilized somehow, even if it's just by creating a stable reference voltage while leaving the main supply voltage unstable.

However, it's likely easier to first check the power supply to the combination instrument before troubleshooting the instrument itself.

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

"Micha"

Hello Micha,

My suspicion is also that there's a problem with the power supply to the AI system, because I'm getting an error in the memory (00668 - Supply Voltage Terminal 30). Otherwise, the lighting wouldn't be flickering.


But without a schematic diagram, it's nothing.

Rainer.

P.S. I wanted to share this link with you.

http://service-bg.com/AUDI/Articles/usermanuals/