Mercedes-Benz has sought clarification from the FIA on the behaviour of Red Bull Racing's Renault engines - amid suspicions that the reigning champion could be doing something trick with its mapping.
AUTOSPORT understands that Mercedes-Benz has presented the FIA with audio analysis of Red Bull Racing's car on track - which has led it to believe the team may be cutting more cylinders than is allowed when the drivers are off throttle.
Under the current regulations, teams can cut up to four cylinders on engine over-run used when the cars are slowing down.
There were suspicions that the audio analysis showed Renault could be cutting down to three cylinders.
The FIA has conducted detailed analysis of the audio evidence, as well as looking at the French car manufacturer's engine maps, and has found nothing that suggests there is a breach of the regulations.
Mercedes-Benz motorsport boss Norbert Haug said that the issue going forward was simply of understanding what was happening - and whether teams would now have to embark on a rethink of engine behaviour.
"I think that it is the normal business of F1," he said when asked by AUTOSPORT about the engine situation. "If you sense something that you do not understand, you like to ask for clarification. I can understand people who ask that in the case of the [Mercedes] rear wing. But we are not threatening to protest; we just want to understand what is going on.
"It is also a cost issue and you should not run different modes, which I don't think is happening, but you can achieve other means to achieve something similar. All of it is not good for the life of the engine.
"If it would not give you lap time then you would not do it - so if we have to do it, we have to do it. We just want to understand that this is normal business in F1. And if you are not requesting that clarification then you are not doing your job. This is not a threat of being illegal; it is just clarification. I am very open and straight on that."