The Bombay Stock Exchange benchmark Sensex turned weak at mid session today after gaining 179 points in the opening trade. It was trading at 16447, down by 51 points at 1:30 hrs. Similarly, the wide-based National Stock Exchange index Nifty fell 25.75 points to 4,872.65 at the same time. Heavy-weights like Hero Honda, BHEL, Infosys and MarutiSuzuki was pulling down the indices, although Finance Minister Pranab Mukherjee said that stimulus measures would continue till there were firm signs of global recovery.