Mr Leu'u said he waited and then tried to use a new radio telephone system to contact the communications centre on Lambton Quay.
When that was unsuccessful, he decided to walk back to the nearby Kilbirnie depot.
Mr Leu'u told passengers what he was doing, put the bus in neutral gear with the motor running and the handbrake on, then left the bus at the shops, the authority said.
When Mr Leu'u arrived at the depot he explained to his supervisor what had happened.
He was then taken back to the Kilbirnie shops where he had left the bus parked.
Meanwhile a passenger on the bus had called Metlink and advised them that the original driver had walked off, the relief driver had arrived and the bus was now continuing on its route.
That day Mr Leu'u's supervisor asked him to complete an incident report, outlining what happened, which was not completed until June 13, the authority said.
Mr Leu'u, accompanied by a member of his union, attended two disciplinary meetings in early June.
Mr Leu'u explained how he had difficulty using the new radio telephone system on the bus, but admitted to leaving the engine running on the bus when he left it at the Kilbirnie shops.
Mr Leu'u maintained he did not abandon the bus, but left it in order to advise his employer of the problem.
At this time, Mr Leu'u was on his final written warning for a safety related incident involving speeding while driving a bus.
A final investigation meeting took place on June 24 and Mr Leu'u was dismissed by WCTL effective immediately.
Authority member Trish McKinnon said WCTL had valid reasons for finding Mr Leu'u's actions constituted serious misconduct.
"It defies common sense for a driver to walk away from a bus with the engine running, keys in the ignition and passengers left to their own devices.
"Wellington City Transport Limited trading as GO Wellington was justified in dismissing Mr leu'u for serious misconduct."
Costs were reserved.
Wellington Tramways Union secretary Kevin O'Sullivan, who represented the former driver at his hearing, said Mr Leu'u was too upset to discuss events.
He said the union accepted the ruling and would not appeal against it.
"We thought we might have some possibility of getting him his job back but we'll live with that decision," he said.