Dundalk Circuit Criminal Court has been told that oil in an engine intercooler could have caused an accident in which two young children died.
Their aunt, Vera Murden, is on trial for dangerous driving causing the death of four-year-old Jenna Murden and her one-year-old brother Jayden on 31 January 2009.
Ms Murden denies the charge.
The accident occurred on a Saturday afternoon when the Hyundai Santa Fe driven by Ms Murden crashed into a wall in Dundalk.
There were five children in the car at the time, four in the rear and one in the front passenger seat.
Today the jury of eight women and four men heard evidence on behalf of her defence.
Consultant Engineer Dr Denis Wood told the court that he had examined the vehicle which had been driven by the accused.
He said he believed the SUV was travelling between 81 and 110km/h when it collided into a wall.
He said he found a small quantity of oil in a groove near one of the inlet points to the engine intercooler.
Dr Wood said Hyundai acknowledged that there could be a number of causes for engines to accelerate or decelerate, including problems with oil in the engine.
The jury had earlier been told by counsel for the defence, Giollaiosa O Lideadha SC, that it was its case that a fault with the engine caused the SUV to accelerate out of control, causing the accident.
Under cross examination by Jonathan Kilfeather SC for the prosecution, Dr Woods acknowledged that he saw no evidence that the rear seat belts had been in use at the time of the crash.
Nor was there any sign of child seats or booster seats in the vehicle, he acknowledged.
The witness admitted that ideally, the children should have been restrained.
The trial is expected to continue tomorrow.
