Renault, engine supplier to reigning world champions Red Bull, has admitted it has kicked off F1's radical new V6 era with a significant problem.
"Obviously we do (have a problem)," the French marque's Remi Taffin told reporters at Jerez on Wednesday.
World champion Sebastian Vettel had left the southern Spanish circuit with only a handful of laps under his belt with the title-defending RB10, while key Mercedes and Ferrari-powered rivals collected far more mileage.
"Annoying!" Red Bull's Dr Helmut Marko told Bild newspaper.
"The problem is in the communication between the two KERS systems," he explained. "So, like in a computer if the hardware and software are not working with each other."
Also struggling are Renault's other F1 customers, including Toro Rosso, the Red Bull sister team whose new STR9 failed even to emerge from the pits on Wednesday.
Caterham is the other affected Renault team.
"The (Renault) cars sound like rattling lawn mowers," said veteran F1 correspondent Roger Benoit, in Blick newspaper. "Renault was even thinking about not coming here."
Taffin, however, is confident the problem can be fixed.
"We've got the parts, we have the people, we have the means to solve the problem," he insisted. "We are confident that tomorrow (Thursday) morning at 9am, our customers will take to the track.
"This is high technology, which is why we have to be cautious. But I am happy with the solution we have found," added Taffin.
Crucial track time already lost, however, Red Bull is now having to look ahead to the second test in Bahrain.
Team boss Christian Horner played down the impact.
"Our expectations coming into this test are purely system checks -- the proper testing will be in Bahrain," he is quoted by F1's official website.
Horner denied that Red Bull is already pushing for the Jerez test to be extended into Saturday, but there are also rumours Renault is paving the road for a delay of the FIA's 'power unit' homologation deadline.
"We will be relying extremely heavily on our engine partner," admitted Horner.
Video with terrible performance of the Renault engine: Vettel is testing the Red Bull RB10 on Jerez day 1