New interior materials and the midyear addition of a performance-oriented Red Line model highlight Ion's '04 changes. Ion is available in sedan and 4-door "Quad Coupe" forms in three trim levels numbered 1, 2, and 3. These share a 140-hp 4-cyl engine and 5-speed manual transmission. Two automatic transmissions are available. Sedans get a conventional 5 speed. Coupes use a continuously variable unit (CVT) with near-infinite gear ratios. Added midyear was the Ion Red Line coupe with a supercharged 205-hp 4 cyl, mandatory 5-speed manual, sport suspension, and 17-inch wheels vs. 14s, 15s, or 16s on other Ions. Head-protecting curtain side airbags are optional on all models; torso side airbags are unavailable. The 1, 2, and 3 models have front-disc/rear-drum brakes; Red Line has 4-wheel discs. ABS is standard on Red Line, optional on the others, and includes traction control. Ion's Quad Coupe has two rear-opening half doors behind the front doors. They do not open or close independently of the fronts. Ion locates its instruments in the center of the dashboard rather than in front of the driver. Split folding rear seatbacks are standard. The coupe's front passenger seat folds forward to create a 10-foot-long storage channel. Leather upholstery is optional on 3 sedans and coupes. A newly available MP3 option upgrades the existing CD player to read discs recorded in MP3 format. All Ions have revised interior trim with new "soft touch" surfaces.