Toro Rosso once again found themselves behind schedule in Bahrain, this time due to a technical failure with the STR9.
One of the teams in need of track-time after too many Renault engine issues, Daniil Kvyat was behind the wheel on the opening day of the final test.
The Russian had a solid morning at the Sakhir circuit, running updates that Toro Rosso plan to use in the Australian GP.
However, shortly after the lunch break, the STR9 had a "technical failure" which meant Kvyat was not able to return to the action.
He finished the day 3.952s down on Sergio Perez's P1 time and with just 56 laps to his name.
"It was nice to be in the car, even if we didn't get through the entire programme we had planned for today," he said.
"However, I feel we have made some progress.
"We ran the hard Pirelli most of the time, as we were definitely not chasing performance today.
"I hope Jev manages to get a full day's running tomorrow, before I drive again on Saturday."