Temperature Reading Error: Troubleshooting Guide

Hello,

Vehicle: Volkswagen Golf IV Convertible, 2.0 gasoline engine.
MKB: AWG

The water temperature gauge has been malfunctioning for a few months.
You're driving, the engine is warm, and the temperature gauge reads 90°.
Occasionally, during the drive, the display will either drop to zero completely, or sometimes it will decrease to a value between zero and 90°. The speed at which the display drops is also variable; sometimes it happens as quickly as when the ignition is turned off, but other times it takes several minutes for the display to settle at the lower level.

This behavior only occurs sporadically and is not reproducible. However, the driving characteristics and fuel consumption are not affected at all when the water temperature gauge drops.

"Does anyone recognize this behavior? Could this behavior be caused by a faulty instrument cluster? I took a Screenshot with VAG-Com about 20 minutes into a drive earlier (see attachment)."

Unfortunately, I am missing a label file for the AWG motor. In addition to the water temperature sensor, the motor also has an oil temperature sensor as standard equipment.
If the displayed 45°C were coming from the water temperature sensor, it would clearly indicate that it is defective. The 94.5° would then likely be from the oil temperature sensor. However, at that time, the combined instrument only showed 84° oil temperature. Everything is a bit strange. While the Screenshot was being taken, the engine was idling, and the water temperature gauge was fluctuating, oscillating between 90°C and approximately 70°C.

Quote:

Everything is a bit strange. While the Screenshot was taken, the engine was idling, and at the same time, the water temperature gauge was "pulsating," fluctuating between 90 and approximately 70°C.

Since it's a wear part at VW, I would replace the temperature sensor first.
The approximately 45° could represent the exhaust air temperature.

Hi!

I'm having the same problem with the temperature gauge, but in my case, it only happens during the warm-up phase. Once it reaches 90°C, the needle stays there. Before that, it's a wild fluctuation .

It's definitely the temperature sensor.
It is easier to find in gasoline engines than in diesel engines.

Best regards,

Take a look inside the control panel housing to see if there's a fault. The temperature sensor is usually located there.
I think it's the temperature sensor.

Thank you for your responses.

Unfortunately, I am unable to log in to the instrument cluster because the control unit 17 is not present.

I'll just go ahead and replace the temperature sensor next week and see if that improves things.

Greetings.

Unfortunately, no sensor error is stored in the memory. At least, that was my experience.
I've been dealing with this "problem" for quite some time. Every time I visited a workshop, I also had them read the error codes. But every time, nothing came up (0 error entries).
I've already replaced the sensor (it's not that expensive), and the "problem" has been resolved. The gauge now rises normally (without any erratic fluctuations).

Best regards,

Thank you all.

I replaced the temperature sensor, and now the display is working perfectly again.

Okay, one more quick question: In the image I posted, what does the lambda value in % indicate? (I have a pre-cat and a post-cat sensor).

Best regards, Daniel.