Hyundai Motor Group (China) Ltd. started recalling some of its imported Rohens cars on Monday, due to problems with the hydraulic electronic control unit (HECU), China's quality watchdog announced on Monday. The recall will involve 1,547 vehicles produced between April 8, 2008 and March 16, 2012 and sold to the Chinese mainland, the General Administration of Quality Supervision, Inspection and Quarantine said in an online statement. The chemical reaction in the HECU of the defective vehicles has affected the proper working of the plunger piston, the statement said. The manufacturer will offer free checks and replace the brake fluid in the recalled cars starting on Monday. Hyundai Motor Group (China) Ltd. is a subsidiary of Hyundai Motor Group, a leading car producer in the Republic of Korea.