water in fuel

Does it happen only when it rains?

Dunno about GM, but with the RAM sensors, water getting through broken insulation on the sensor wires will cause the light to go on.

For a while the sensors had poor strain relief where the wires entered the sensor, and this could happen. Newer sensors have this fixed.

These new trucks have so many sensors and computers, they often require an electronic or computer technician to fix, not a mechanic.

As far as I know we don't have a lot of BioDiesel stations in Ontario and the likelihood of getting a bad fill is pretty far down the list too. In 40 year of driving diesel in Canada I've never had the light come on, even draining is bit has been a waste of time.

This would happen with a fair degree of regularity with the 05 LLY Duramax we had. I replaced the WIF sensor with no effect on the issue. Best I ever came up with is that there is a variance in the density of the fuel. Likely caused by the percentage of Biodiesel blended. I so far have not seem this with the 18 Duramax truck.

You probably have a bad water sensor. You do get the prize for finding that one bad unit statistics predicts is out there, no matter how well designed and built or how thoroughly tested a product is. Oh, your prize? A trip to the truck store for repairs. Should be covered under warranty.

I don't use my diesel farm tractors in the winter, they stay in the unheated barn so condensation in the fuel tanks has always been an issue and the tractors all have a readily visible separator with a float on the side of the engine.

Been using Powerservice in them for at least 10 years and no water in the separators every.

Same regimen with my pickup truck. It gets parked all winter too.

You get to do some maintenance. Drain your fuel filter. Get some diesel additive in the white container available at any truck stop.