Courtney had set the 20th fastest time in the eight-minute session that determined the grid for the Sunday race, but will now start last.
The rear wing angle on the #7 Mustang was found to be 10.2 degrees, which is 0.2 degrees above the maximum permitted.
According to a stewards document seen by Speedcafe, BRT did not dispute the process or the measurement recorded.
“The [team] representative advised the team had made a change to the rear wing angle prior to the first qualifying session (Race 6) to 9.5 degrees,” read the report.
“Then another adjustment to the rear wing was made prior to the commencement of the second qualifying session (Race 7) by lifting the rear wing one notch higher prior, noting the team didn’t have time to check the angle.”
It’s the latest blow in a horror weekend for the Snowy River Caravans-backed driver.
Courtney missed both Thursday qualifying sessions and that evening’s race after a heavy crash in practice.
The 2010 champion drove from last to 17th in Friday’s race and will start 23rd this evening, sharing the last row of the grid with teammate Aaron Cameron.
Debutant Cameron has also had a rough run, finishing the opening two races in 22nd and 19th.
Cameron managed 24th and 23rd in the two Saturday morning qualifying sessions and will be elevated one grid spot for Sunday due to his teammate’s trouble.
This evening’s Race 6 of the season will take place from 5:40pm local time.