Toro Rosso, which topped the mileage chart last week, suffered a setback today, with Pierre Gasly achieving just one lap in Monday's afternoon session.
The Frenchman had put 57 trouble-free laps under his belt in the morning and was aiming for more of the same after the lunch break, but a brake system issue kept the STR13 in its garage.
"This morning went super-well, but this afternoon a small issue on the brake system cost us quite a lot of time because we didn’t run at all in the afternoon," Gasly said.
"It was a bit of a shame, but hopefully we can sort everything out for the next three days.
"In terms of performance, it’s too early to say because we didn’t really run in qualifying mode, so it’s difficult to compare with what we had last year.
"But at the moment, the only thing we need is to have a reliable engine and to test as much as we can before Melbourne. We are really happy so far.”
Brendon Hartley is expected to resume Toro Rosso's test programme on Wednesday.
"Our programme this week is more race focused," said Honda technical director Toyoharu Tanabe.
"Unfortunately we lost some track time, stopping running in the afternoon because of an issue with the car.
"Identifying problems like this is what testing is for and we will make further preparation to make up the lost time over the remaining three days."