Mercedes called a halt to their first day of Formula One testing on Tuesday after Nico Rosberg stopped on track with flames flaring briefly around the back of his car.
The team blamed an electrical fault.
"The part which requires modification is the wiring loom where the electrical fault originated this morning."
Rosberg completed 14 laps at the Jerez circuit in the F1 W04 car that he and new team-mate Lewis Hamilton unveiled to the world on Monday.
Hamilton, the 2008 world champion who has moved from McLaren, is due to have his first proper run in the car on Wednesday.
Mercedes were fifth overall last season and the Briton, who replaces Germany's seven-times world champion Michael Schumacher, could have a hard road ahead of him before the regulations change in 2014.
Meanwhile, over at the McLaren camp, Jenson Button's redesigned MP4-28 sputtered to a halt 10 minutes into testing with suspected fuel delivery problems.
The 2009 world champion helped team workers cover the car before a truck arrived to transport it back to the pits. By early afternoon the Briton had yet to complete a competitive lap.
Reuters & Sapa-AP