No the MPG system does not take into account the booster heater.....it does not know that it exists....therefore your MPG will be lower than that seen on the readout. The cars electronics can measure the speed of the vehicle and also the engine fuel consumption, from this it can easily calculate the approx. MPG of the vehicle. It is not 100% accurate even over long distances. Also it can be severely affected by the variation by any deflation, wear and modifications of the vehicles tyres.