Raikkonen was second on the first day of testing in Barcelona, just 0.007s shy of Nico Rosberg's Mercedes.
The Finn completed forty laps at the home of the Spanish Grand Prix.
"It wasn’t an ideal day in terms of the number of laps we completed, but the car feels strong and we’ve made some good progress," he said.
"After Jerez it’s nice to be at a circuit where we race and the E21 is definitely a step in the right direction. There’s lots of work yet to do this week but I’m happy with where we are at the moment."
Raikkonen returns to the cockpit tomorrow.