Does this Costco have diesel fuel?

Costco in Rancho Cucamonga does not have Diesel. Kirkland Signature Diesel is available at select Costco locations. You may find it at https://www.costco.com/gasoline-diesel.html

I never seen it beforehand

Not that I know

Costco does not sell diesel fuel. They only carry regular and premium Gas. It nationwide policy

Yes they do.

I recall a second nozzle, but I've gone to do many Costco has stations, I think if just call them first