Sebastien Bourdais' post-race victory doughnuts at Milwaukee last week have been labelled the likely cause of his car subsequently being found to be under IndyCar's minimum weight.
The Frenchman's KV Racing team was fined $5000 after the car failed the technical inspection, coming in below the mandated 1600lb.
While IndyCar did not provide any additional information about the infraction, it did say in a statement that the relatively small punishment reflected the minor nature of the breach.
However IndyCar president of competition and operations Derrick Walker told AUTOSPORT in Iowa that the car was three pounds (1.3kg) underweight, and identified Bourdais's post-race celebration as the culprit.
"We think it was all of those doughnuts that he did," Walker said.
"He took all the rubber off the tyres. The car was likely the correct weight when it crossed the finish line, so there was no competitive advantage.
"The fine is in line with what we've done in the past - when there's a minor technical breach that doesn't translate into a competitive advantage, we tend to impose a financial penalty rather than something more severe."