To get fuel consumption settings of a unit, use the command unit/get_fuel_settings:

svc=unit/get_fuel_settings&params={"itemId":<long>}

{
	"calcTypes":<uint>,		/* method of calculating fuel consumption (see below) */
	"fuelLevelParams":{		/* detection of fuel fillings/thefts */
		"flags":<uint>,			/* flags of fillings and thefts (see below) */
		"ignoreStayTimeout":<uint>,	/* ignore the messages after the start of motion, sec */
		"minFillingVolume":<double>,	/* minimum fuel filling volume, litres */
		"minTheftTimeout":<uint>,	/* minimum stay timeout to detect fuel theft, sec */
		"minTheftVolume":<double>,	/* minimum fuel theft volume, litres */
		"filterQuality":<ubyte>,	/* filter quality (0..255) */
		"fillingsJoinInterval":<uint>,	/* timeout to separate consecutive fillings, sec */
		"theftsJoinInterval":<uint>,	/* timeout to separate consecutive thefts, sec */
		"extraFillingTimeout":<uint>	/* timeout to detect final filling volume, sec */
	},
	"fuelConsMath":{		/* consumption math */
		"idling":<double>,		/* idling, litres per hour */
		"urban":<double>,		/* urban cycle, litres per 100 km */
		"suburban":<double>,		/* suburban cycle, litres per 100 km */
		"loadCoef":<uint>		/* coefficient when moving under load */
	},
	"fuelConsRates":{		/* consumption by rates */
		"consSummer":<double>,		/* summer consumption, litres per 100 km */
		"consWinter":<double>,		/* winter consumption, litres per 100 km */
		"winterMonthFrom":<uint>,	/* winter from (month: 0-11) */
		"winterDayFrom":<uint>,		/* winter from (day 1-31) */
		"winterMonthTo":<uint>,		/* winter to (month 0-11) */
		"winterDayTo":<uint>		/* winter to (day 1-31) */
	},
	"fuelConsImpulse":{		/* impulse fuel consumption sensors */
		"maxImpulses":<uint>,		/* max impulses */
		"skipZero":<uint>		/* skip first zero value */
	}
}

Method of calculating fuel consumption:

Flags of fillings and thefts: