Power leads opening test session at Sonoma
| Rank | Car | Driver Name | Engine | Time | Diff | Gap | Laps |
| 1 | 12 | Power, Will | CHEVY | 01:18.1099 | –.—- | –.—- | 4 |
| 2 | 15 | Rahal, Graham | HONDA | 01:18.4460 | 0.3361 | 0.3361 | 5 |
| 3 | 10 | Kanaan, Tony | HONDA | 01:18.4554 | 0.3455 | 0.0094 | 4 |
| 4 | 27 | Andretti, Marco | HONDA | 01:18.4620 | 0.3521 | 0.0066 | 5 |
| 5 | 14 | Munoz, Carlos | CHEVY | 01:18.5439 | 0.4340 | 0.0819 | 4 |
| 6 | 5 | Hinchcliffe, James | HONDA | 01:18.5443 | 0.4344 | 0.0004 | 6 |
| 7 | 18 | Bourdais, Sebastien | HONDA | 01:18.6481 | 0.5382 | 0.1038 | 5 |
| 8 | 20 | Pigot, Spencer | CHEVY | 01:18.8692 | 0.7593 | 0.2211 | 6 |
| 9 | 83 | Kimball, Charlie | HONDA | 01:18.9144 | 0.8045 | 0.0452 | 15 |
| 10 | 8 | Chilton, Max | HONDA | 01:18.9611 | 0.8512 | 0.0467 | 7 |
| 11 | 19 | Jones, Ed (R) | HONDA | 01:19.1016 | 0.9917 | 0.1405 | 8 |
| 12 | 13 | Claman DeMelo, Zachary (R) | HONDA | 01:19.3032 | 1.1933 | 0.2016 | 32 |
| 13 | 7 | Harvey, Jack (R) | HONDA | 01:19.4493 | 1.3394 | 0.1461 | 13 |
| 14 | 4 | Daly, Conor | CHEVY | 01:20.1927 | 2.0828 | 0.7434 | 11 |