The court heard there was no evidence Morehu's truck swerved or braked before colliding with the bus, shunting it 80m through a fence and into a paddock.
A blood sample was found to contain tetrahydrocannabinol - the active ingredient of cannabis.
Morehu had also started work at 4am, resting for less than two hours, and made omissions to his log book.
Three months later, Morehu crashed a car. He was later processed with 165mg of alcohol per 100ml of blood.
But as it was his first time before the courts, Judge Wolff told him it was unlikely he would receive a jail sentence when he appears again on July 4.