Nico Rosberg retirement due to foreign substance - Mercedes

Mercedes say Nico Rosberg's retirement from the Singapore Grand Prix was caused by his car being contaminated by a "foreign substance".

The team said analysis of the German's steering column revealed a residue of a material used in pre-event servicing.

This caused a short-circuit that led to the problems Rosberg encountered before and during the race with using his clutch and changing engine settings.

The contamination was not visible and did not affect the car until race day.

The team said the substance which affected the column is used in servicing at the factory before the cars are shipped to the races and that the steering column design had been in use since 2008.

Mercedes added in a statement: "Fresh parts will be used at the forthcoming races.

"The team has been working intensively on reliability and quality processes during 2013 and 2014 in order to improve our performance in this area and these efforts will continue at the same intensive level over the coming months."

Rosberg was forced to start the Singapore race from the pit lane because he could not get a gear on the grid.

After running at the tail of the field with no hybrid power and a faulty gear change he retired from the race at his first pit stop when again the car would not move out of neutral.

Rosberg's team-mate Lewis Hamilton won the race, turning a 22-point deficit in the championship into a three-point lead with five races remaining and a maximum of 150 points still available.

The next race is the Japanese Grand Prix at Suzuka on 5 October, live on BBC TV, radio and online.