The EFI light on generally just means there is an error on one of it's inputs. It can be anything including Temp- both coolant or air intake, O2 sensor, fuel pressure, CPS, TPS and a few others. I would go through it and check all the sensor's connections for connectivity, water, corrosion..ect. If nothing it may be a bad sensor and if so, probably have to wait until it fails completely to get the code to know what it is.