The 1.6L Alpha II debuted in 2001, eventually replacing the 1.3L and 1.5L. It was further revised in 2005 with a 1.4L version also debuting. Notable improvements over the Alpha included a DOHC 16-valve cylinder head, graphite-coated pistons, a strengthened cylinder block, ribbed aluminum oil pan, coil-on-plug ignition, an enlarged throttle body (increased from 48 mm to 52 mm), a revised PCM (powertrain control module), simplified and shortened intake ducting, a revised intake manifold, and a returnless fuel system. These improvements further reduced NVH and emissions, with the 1.6L version becoming ULEV-certified in all 50 U.S. states.