No idiot lights going on?
Could be something to do with the evap circuit where the fuel filler neck wasn't completely tightened and not running the right pressure in the fuel system.
There's also some ABS circuits that run in that area, but those should definitely light up something.
Most likely the fuel system/evap circuit throwing a signal about the gas cap not being on, or loose.
Could even be that the fuel lines are loose and you're almost out of gas from leakage. The slower engine speed caused the fuel to slosh forward and raise the float out of the "yo, man, you bettah find a station now or you gon' be ridin the heel-toe express" range.