"To be involved in such a successful debut V8 Supercars season has been incredibly rewarding," said Dahlgren. "I am proud to have played a key role in the development of the new car and engine, linking GRM in Melbourne with Polestar in Gothenburg.
"The entire GRM team - and the Australian motorsport fans - have all been incredibly welcoming to me and my family. The V8 Supercars Championship is without doubt one of the best in the world and I leave Australia with many happy memories."
"At GRM are very thankful to Robert for the assistance and professionalism he has displayed in his 12 month contract with our race team. Said team owner Garry Rogers.
"As much as sheer race results may not indicate the true value of Robert's input, his off track input and work has been very much appreciated, and we wouldn't be where we are today without him.
"Robert has a very good engineering mind and his knowledge on the processes within both Volvo and Polestar have been extremely helpful with our transition to a factory Volvo Polestar team. I wish him, his wife Nina and young son and daughter all the best in their return to Sweden".
The 2015 Volvo Polestar Racing V8 Supercars driver line-up will be announced before the start of the season.