Nunez was signed to drive the sole full-season entry from AXR alongside Pipo Derani after the other half of its 2021 title-winning lineup, Felipe Nasr, departed the squad to join Porsche.
The 26-year-old Floridian, who was previously part of the Mazda DPi programme before it was scaled back to one car ahead of its final season in 2021, spent the 2021 IMSA season in the WIN Autosport LMP2 car and won at Watkins Glen.
But Nunez and Derani have had a disappointing start to the 2022 IMSA season, and ahead of this weekend's Detroit round sit only fifth in the DPi class championship with no finish higher than third.
AXR’s statement says that Nunez will remain on the team as standby driver, but his seat alongside Derani will be taken for the remainder of 2022 by Pla.
Team boss Gary Nelson said: “We are happy to have Olivier join the AXR team starting with the Chevrolet Detroit Grand Prix this weekend.
“The IMSA DPi class is very competitive this year and we want to make sure we can have a strong second half to the season.
“Tristan has done a great job driving the Whelen Engineering Cadillac. All of us at Action Express Racing have developed a great relationship with Tristan and his family.
“He is a young driver with many wins and championships in his future. Tristan remains a major part of this team, and we value having his input on the race weekends to keep moving our programme forward.”
For the 2016 Petit Le Mans winner, also a regular for Glickenhaus in the World Endurance Championship alongside Derani, this will be a chance for redemption after he was released early from his contract with the Meyer Shank Racing Acura squad last year.
The 40-year-old, who tested the AXR Cadillac at Road Atlanta last week, said: “Joining Action Express Racing is very special to me.
“I’ve been racing against them for many years, and I know how good they are on the track. What they’ve achieved by winning so many races and championships speaks for itself.
“It will be a big challenge to arrive mid-season but I’m ready to take on this challenge. The Cadillac DPi-V.R is a fantastic car and I can’t wait to race it.
“And of course, extremely happy and proud to join such a great driver and friend as Pipo Derani!"
