Nico Rosberg's retirement from Sunday's Singapore Grand Prix was caused by a freak contamination of his steering column electronics by a substance used by Mercedes in their pre-event servicing, the team said on Friday.
The Mercedes team said the contamination led to a loom failure in his steering wheel column. This resulted in him struggling to start and then abandoning the race won by team mate Lewis Hamilton.
Briton Hamilton's victory lifted him three points clear of German Rosberg with five races remaining in their sometimes acrimonious duel for the drivers' title.
"Forensic analysis has revealed that the steering column electronic circuits were contaminated with a foreign substance," the team said in a statement.
"This occurred during our normal pre-event servicing procedures at the factory and the substance found is used as part of our standard servicing procedure.
"The contamination was not visible and did not manifest itself until Sunday as Nico went to the grid, although the steering column was used throughout the weekend and the car fired up as normal on Sunday morning.
"Nico could not command the clutch nor change engine settings. The car was ultimately retired because it was unsafe to execute a pit stop without command of the clutch. Fresh parts will be used at the forthcoming races."
The next race is the Japanese Grand Prix on October 5.
