System and method for determining whether an engine is on or off based on a pressure of exhaust gas produced by the engine

A system according to the present disclosure includes a pressure sensor and an engine state module. The pressure sensor is configured to measure pressure in an exhaust gas supply line that supplies exhaust gas from an engine to an emissions measurement system. The emissions measurement system includes a dilution tunnel, a sample probe, and a sample collector. The exhaust gas is diluted with a dilution gas in the dilution tunnel, and the sample probe supplies a portion of the diluted exhaust gas to the sample collector. The engine state module is configured to determine whether the engine is on or off based on at least one of (i) a frequency of pulsations in the exhaust gas supply line pressure and (ii) a magnitude of the pulsations in the exhaust gas supply line pressure.