Speedometer Malfunction G4 1.4 (1999)

In a 1999 Volkswagen Golf IV 1.4, the speedometer is malfunctioning. The speedometer needle sometimes drops to 0, then shows a normal value again, or jumps to a value above 100. It appears to be a loose connection at first glance.
Can the speed sensor be tested by running VAG-Com simultaneously? If the VAG-Com reading is also incorrect, then it's likely the sensor; otherwise, it's probably the instrument cluster, correct? Is there a way to diagnose faults in the instrument cluster, or should it be replaced directly?

'Thank you.'

Yes, you can run VAG-COM in parallel. The easiest way is to check the engine control unit; that will tell you if the sensor data is still being received correctly.

I cannot determine whether you are capable of repairing a station wagon yourself, as it depends entirely on your skills, which I am unable to assess.

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

But in principle, you can open it, and at least check the contacts?

'Can you somehow move the needles on the instrument cluster using VAG-Com? Is it done with a diagnostic tool or something similar (does anyone know exactly how?)? Does it involve faking a signal from the engine control unit, or is it simply manipulating the needles directly?'

As far as I know, a 0-10V voltage is typically used as a tachometer signal. Perhaps you could also simulate this signal using the vehicle's voltage and a variable resistor?

highbeta wrote:

But in principle, you can open it, and at least check the contacts?

Yes, you can.

highbeta wrote:

Using VAG-Com, it's somehow possible to move the needles on the instrument cluster. With a diagnostic tool or something similar (does anyone know exactly how?), is a signal from the engine control unit being simulated, or are the needles actually being physically rotated?

AFAIK, only the pointer itself is being manipulated. However, you can use VAG_COM to check what data the instrument cluster (KI) is receiving from the sensor.

highbeta wrote:

As far as I know, a 0-10V voltage is used as a tachometer signal.

Perhaps you could also simulate this signal using the vehicle's voltage and an adjustable resistor?}
That's news to me. As far as I know, the input is a frequency proportional to the speed. So, it should be possible to simulate it with a function generator. However, you should probably start by checking the simpler things first, like loose connections and VAG-COM values.

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

Hi,

Does only the speedometer display drop to zero for you, or does everything else also stop working? Has the daily mileage counter been reset, or not?

My car's combination instrument panel seems to have a faulty solder joint somewhere in the power supply. Occasionally, all the gauges drop to zero, along with the daily mileage counter. After about a second, they come back on. I just need to find the time to fix it by resoldering.

Best regards,

Jan.