Six IndyCar drivers, including top two in points, face grid penalties
Four others in the 25-car field will face the same penalty, including Firestone 550 winner Justin Wilson.
Power, who has won three races this season, takes a 36-point lead over Dixon into the 225-lap race June 16 (1 p.m. ET on ABC) at the Milwaukee Mile. James Hinchcliffe of Andretti Autosport is third (48 points out) and Helio Castroneves is 53 points arrears of his Team Penske teammate.
"It's going to be hard to win from back there," said Power, whose engine in the No. 12 Verizon Team Penske car ceased in the afternoon session.
There's 90 minutes of practice scheduled June 15 at the Milwaukee Mile preceding two-lap cumulative time qualifications (4 p.m. local).
Dixon's No. 9 Target Chip Ganassi Racing car sustained a failure of its Honda engine with a few minutes left in the morning session of a test at the .875-mile Iowa Speedway on June 12. The crew had installed a fresh engine for the test after contact with the Turn 4 SAFER Barrier on Lap 174 of the Firestone 550 at Texas Motor Speedway on June 9 damaged that powerplant.
Dixon, who won at Belle Isle two weeks ago, had his first DNF since the race in Toronto in 2010. In eight previous starts at Milwaukee in Champ Car and the IZOD IndyCar Series, he has finished in the top 10 seven times — including a victory in 2009 from the fourth starting position.
Last year at Milwaukee, Power advanced 13 positions relative to his starting spot to finish fourth. In two other starts on the historic oval (one each in Champ Car and the IZOD IndyCar Series, he has a best finish of 11th in '06 with RuSport).
Additionally, A.J. Foyt Racing's No. 14 ABC Supply car driven by Mike Conway will serve the 10-grid spot penalty for the second consecutive race as its engine quit at the Iowa test. Wilson's engine in the No. 18 Sonny's BBQ car for Dale Coyne Racing gave out at Iowa, too.
The No. 15 Rahal Letterman Lanigan Racing car of Takuma Sato and the No. 67 Sarah Fisher Hartman Racing car driven by rookie Josef Newgarden also will receive 10-spot grid penalties for unapproved engine changes at Texas.