After the ute he was driving lost control and plunged off a Cambridge road into the Waikato River - fatally injuring his girlfriend - Derek Keesing insisted the brakes had failed.

"The first thing I know is I applied my brakes and I am absolutely positive I had no brakes. My foot went to the floor," he told police after the crash on Saturday, August 19, 2017.

But by the time of his sentencing in the Hamilton District Court on Friday, Derek Ivan Keesing, 61, had changed his tune.

He conceded there had been no mechanical mishap with the 2014 Nissan Navara and it was excessive speed that led to the death of Susan Donna Ramsay, 60.

The former Tīrau Community Board member was sentenced to six months of community detention and disqualified from driving for nine months, and was ordered to pay $7500 in reparation to the family of Ramsay, who died in Waikato Hospital two days later as a result of a brain injury.

What Judge David Cameron described as "a tragic incident" happened at 12.25pm as Keesing headed west on Tīrau Road in Cambridge, approaching the roundabout at Shakespeare Street.

He hit the raised traffic island and the ute, along with the trailer it was towing, smashed through a protective railing and plunged down the steep bank and into the turbulent, 12-metre-deep water.

"Those are the sad facts," Judge Cameron said. "The degree of carelessness is at least moderate."

Having earlier pleaded guilty to a charge of careless driving causing death, Keesing came to court with no previous convictions and five references attesting to his good character.

He and Ramsay had been in a relationship for about six weeks before the crash. As defence counsel David Allen put it, the pair were inseparable, bonded by their shared love of Ford Thunderbirds.

Keesing, a self-employed electrician, suffered head and knee injuries in the crash and "is still struggling emotionally", Allen said.

"He can't undo what has happened. He is deeply sorry for that."

He wanted to participate in a restorative justice conference with Ramsay's family, but they were not keen.

Despite that, Keesing was eager to liaise with them about the possibility of creating some sort of memorial for Ramsay, and had $7500 he could pay to her family immediately.

While Ramsay's family had expressed reservations about accepting that money, the judge ordered it be paid regardless of whether they made use of it themselves or simply gave it away to charity.

-Stuff/Mike Mather.