Will Power's best lap hit 215.761mph, followed by Ryan Briscoe (215.133mph) and Josef Newgarden (214.948mph). In total, 22 cars took part and notched up 2594 laps between them during the day. Air temperatures reached a high of 31.7C (89F) during the afternoon, and dropped to 25.6C (78F) under the floodlights after dusk by the time the session ended, which is when the race will finish on Saturday.
"It's a good start to the weekend," said Power. "The car was good and we just kept getting better and better as the day went on. I think we're in pretty good shape for qualifying. We're ready. Now we just need to go out and get it done."
EJ Viso ran just 40 laps during the day before making contact with the wall. Ryan Briscoe's day also ended in contact, but in his case it was right as the session came to an end in any case.
“I just got on the high line and hit a bump at the entry of turn 3 and it just spun around," explained Briscoe. "Aside from the impact at the end, it was a really good test day overall."
The series hasn't raced at Fontana since 2005 and the one-day test is to allow drivers to get some extra familiarisation time on the circuit before the start of formal practice, which begins with a 90 minute first session on Friday morning.
The qualifying session follows in the afternoon, with a further 45 minute practice session then scheduled for early evening to match the 5.45pm PST (1.45am BST) start time for the MAVTV 500 IndyCar World Championship race itself on Saturday evening, which is expected to last up to three hours before the chequered flag is due to drop shortly before 9pm (5am BST).