191 919 376A is the VW Coolant Level Warning Lamp Control Module. I traced the schematic and then found that it's already been done.
This is how it works.
The IC is custom, so fixing one of these would be tricky. Except maybe with a PIC? You could probably do something with an LM1830 and a 555, but it'll be kind of complex I suspect.
I found that my module was too sensitive, or maybe not sensitive enough, depending on how you look at it. The resistance of my coolant mix is not low enough to pull pin 5 low and attenuate the signal enough. So even with sufficient coolant, my LED would blink. I solved this by adding a second 68k resistor in series with the one connected to pin 2.
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