F1 heads to Spain on Wednesday for pre-season testing with Valtteri Bottas, Charles Leclerc and Max Verstappen all putting in the first official laps.
Unlike last season when Williams wasn’t present for two days, all 10 teams are expected to be in action on Wednesday morning.
But how much action each team does will depend on reliability.
With the running reduced to just six days this year, Haas driver Romain Grosjean has highlighted the importance of a trouble-free test.
He told Motorsport.com: “Last year, we had a lot of electrical problems when it was just a fuse somewhere that was bothering us, and it put us out of action for whole mornings.
“Now, we can’t afford to have that.
“We have to have the car working. We have to drive it and push it on a little bit, in all possible circumstances, to be ready so we know what to do at the races.”
The opening test takes place from Wednesday to Friday with the teams in action from 9am to 1pm before resuming running from 2pm to 6pm.
Merceedes, Renault, Racing Point and Williams have all decided to split Wednesday’s opening day between their two race drivers while first up for Alfa Romeo will be test driver Robert Kubica.
The Polish driver is the only tester down on the schedule to put in laps this week.
Meanwhile Ferrari, Red Bull, McLaren, AlphaTauri and Haas will run just one driver on Wednesday before their respective team-mates take over on Thursday.
Ferrari were due to work with Sebastian Vettel on Wednesday but illness has ruled him out and so Charles Leclerc takes his spot instead.
Mercedes: Valtteri Bottas (morning), Lewis Hamilton (afternoon)
Ferrari: Charles Leclerc
Red Bull: Max Verstappen
McLaren: Carlos Sainz
Renault: Esteban Ocon (morning), Daniel Ricciardo (afternoon)
AlphaTauri: Daniil Kvyat
Racing Point: Sergio Perez (morning), Lance Stroll (afternoon)
Alfa Romeo: Robert Kubica (morning), Antonio Giovinazzi (afternoon)
Haas: Kevin Magnussen
Williams: George Russell (morning), Nicholas Latifi (afternoon)