The faulty part is in the brakes' vacuum servos in some A4, A5, A6 and A7 sedans, and Q5 and Q7 sports-utility vehicles made between March and December 2012, a spokesman for the German premium car maker said.

Oil may enter the vacuum servos of these cars so that drivers have to press the brake pedal stronger, he said.

Write to Ilka Kopplin at ilka.kopplin@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires