A harvesting vehicle including a cleaning section including a blower and at least one sieve. The sieve is configured to transport a layer comprising a mixture of grain kernels and residue material towards an exit edge of the sieve so that kernels fall through openings of the sieve and the residue remains on the sieve until it is ejected from the sieve by crossing the exit edge. The sieve may be subject to a grain loss, including a sieve-off loss and a blowout loss. The cleaning section further includes a sensor configured to determine whether the blowout loss or the sieve-off loss is a highest contributor to the grain loss. The cleaning section may also include a grain loss detector configured to measure the sieve-off loss and at least a portion of the blowout loss and a blowout sensor mounted above the sieve for measuring the blowout loss.