X0305 4 2012-05-10 0 0000949428 CLEAN DIESEL TECHNOLOGIES INC CDTI 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 2012-05-10 4 S 0 20781 3.0022 D 1104413 I By Limited Partnerships This is a weighted average price. This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP), Special Situations Cayman Fund, L.P. (Cayman), Special Situations Private Equity Fund, L.P. (PE), Special Situations Technology Fund, LP. (TN) and Special Situations Technology Fund II, L.P. (T2). 552,206 shares of Common Stock are held by QP, 176,707 shares of Common Stock are held by Cayman, 69,277 shares of Common Stock are held by PE, 42,670 shares of Common Stock are held by TN and 263,553 shares of Common Stock are held by T2. The interest of Marxe and Greenhouse in the shares of Common Stock owned by QP, Cayman, PE, TN and T2 is limited to the extent of his pecuniary interest. Austin W. Marxe 2012-05-14 David M. Greenhouse 2012-05-14