According to my manual, the fuel light goes on when the tank is down to approx 6 litres of diesel.
My Mk3 fiesta did not.
water sensor has malfunctioned/or fuel has large quantity of water contamination.
Diesel engines run on diesel fuel. Gasoline will destroy a diesel engine.
A 1998 Ram with the Cummins diesel has a water in fuel indicator on the dash that will illuminate if there is water in the fuel filter housing.
Where is the water drain for the Water in Fuel light?
Yes, diesel is a bio fuel
Diesel fuel can appear different colors due to variations in its composition and any added dyes. Typically, diesel fuel is a light yellow or pale green color. However, impurities, contaminants, or oxidation can darken its color. Additionally, some countries regulate the color of diesel fuel for tax or identification purposes, leading to variations in color.
If the van has a diesel engine, then you MUST use diesel fuel. Unleaded gasoline will destroy a diesel engine. Diesel fuel is also used as a lubricant in a diesel engine. The use of any other fuel except diesel will result in serious damage. If you have put unleaded in your diesel, do not start or drive this vehicle until you drain the tank and change all the fuel filters.If the van has a diesel engine, then you MUST use diesel fuel. Unleaded gasoline will destroy a diesel engine. Diesel fuel is also used as a lubricant in a diesel engine. The use of any other fuel except diesel will result in serious damage. If you have put unleaded in your diesel, do not start or drive this vehicle until you drain the tank and change all the fuel filters.
Normally that would be the low fuel warning light
Where is the diesel fuel filtered
Water is heavier than diesel fuel