Defence lawyer James Rapley questioned the reliability of the Crown's key witness, Reece Dick-Durham, 18, who was the only passenger in the car besides Redeemed to have survived the crash.
Mr Dick-Durham earlier this week testified that Redeemed had leaned over to look at the oncoming bus before grabbing the wheel with his right hand, and steering the car into the other lane.
He said Redeemed then tried to steer the car away from the bus but it was "too late" and the vehicles collided.
The defence case is that Redeemed did not grab the wheel of the car.
Mr Rapley said it was not a case of his client versus the witness, nor was he seeking to belittle or discredit Mr Dick-Durham.
But he questioned how reliable and accurate Mr Dick-Durham's testimony was, asking whether he had mixed up the crash with events earlier that day.
"Reece's memory is poor and flawed and missing major events of that journey," he said.
"Can you trust the same memory for what happened just before the car hit the bus?"
The car's driver, Mr McCartney, was drunk and its occupants had been "fooling around" before the crash.
Mr Rapley referred to other witnesses who said the car had been driven dangerously, at one point crossing the centre line for three to four seconds, and at another point taking a corner so fast that its wheels left the road.
Mr Dick-Durham had no memory of those events and it was possible he had "muddled the order" of events, said Mr Rapley.
The defence lawyer also questioned Mr Dick-Durham's testimony that Redeemed had tried to steer the car out of the path of the oncoming bus, which he said contradicted evidence from the Crown's own witness.
Mr Rapley said that was "troubling" and the last seconds of Mr Dick-Durham's memory were false.
Crown prosecutor Claire Boshier said Mr Dick-Durham's memory was reliable because he had come so close to death, the Dominion Post reported.
Mr Dick-Durham was asked 13 times under cross-examination whether he was mistaken but he was adamant he was not.
He denied mixing up the crash with an earlier incident in which Redeemed allegedly grabbed the wheel of another car and said, "I could end it now."
The jury will begin deliberation tomorrow after the judge sums up.
The trial was moved to Wellington from Christchurch because of earthquake damage to the court building.