VW T5, Audi A3, A4, etc.: Coolant level warning due to freezing temperatures (Solution)

Subject:
All vehicles from the VAG group manufactured approximately before 2006, which were originally filled with G12 or G12+ coolant AND have the coolant level sensor permanently integrated into the expansion tank.
"When changing the coolant later (e.g.,..." Even after repair, etc., on G12++, the phenomenon can still occur.

Complaint:
At temperatures below approximately -5°C, a coolant overtemperature/low level warning (red warning light) appears about 10 seconds after a cold start, even though the coolant level is within the normal range. O. (presumably referring to an indicator or reading) is also well below the warning threshold, and the engine temperature is significantly lower than the warning limit.
The error can also occur sporadically, but it always disappears after restarting the engine, even if the engine temperature is only slightly warm. B. 1 minute runtime.

Cause:
Due to an oxide layer on the coolant level sensor and simultaneously increased coolant resistance at very low temperatures, the resulting low conductivity is interpreted by the control unit as a coolant shortage and reported via the fault information system (FIS), multifunction display (MFA), or maintenance indicator (MIL).
As the coolant temperature approaches the freezing point of water, the engine control unit (ECU) will correctly recognize the proper coolant level again.

Fix:
Replace the coolant reservoir and refill with coolant of type G12++.
The sensor is permanently integrated into the coolant reservoir and therefore cannot be removed, installed, or replaced individually.
The coolant additive G12++ is designed to prevent renewed oxidation of the coolant over its lifespan.

Best regards from the DBär .