The first fourth-generation Acura TL rolled off the assembly line on September 23, 2008. Debuted for the 2009 model year, the Acura TL featured a more aggressive interpretation of Acura's latest styling vocabulary, known as "Keen Edge Dynamic." Featured prominently on the front is Acura's controversial "Power Plenum" upper grille. The size of the car has increased slightly, and as a consequence the wheelbase has been stretched 1.4 inches (36 mm) to 109.3 inches (2,780 mm). The car is also 6.2 inches (160 mm) longer overall, 1.8 inches (46 mm) wider and 0.5-inch (13 mm) taller. Rear legroom improves by 1.3 inches (33 mm) and rear shoulder room increases by 0.5-inch (13 mm). Structural rigidity was increased due to the use of high-strength steel in 47.6 percent of the chassis.
The base TL is front-wheel drive and is powered by a 3.5-liter V6 that makes 280 hp (210 kW) and 254 lb·ft (344 N·m) of torque, an increase of 22 hp (16 kW) and 21 lb·ft (28 N·m) over the previous 3.2-liter V6. The new TL SH-AWD ("Super-Handling All-Wheel Drive") replaces the previous TL Type-S and is powered by a 3.7-liter V6 that produces 305 hp (227 kW) and 275 lb·ft (373 N·m) of torque, an increase of 19 hp (14 kW) (Acura originally advertised the car as having 307 hp (229 kW), but revised that claim without any explanation after a few months on the market) and 19 lb·ft (26 N·m) over the 3.5-liter V6 of the Type-S. The 3.7L engine also uses VTEC variable-lift timing on both the intake and exhaust valves (the base TL and previous models only applied VTEC to the intake valves).
SH-AWD ("Super Handling" All Wheel Drive) is a multi-vectoring all wheel drive system designed more for performance than for simply providing traction in adverse circumstances. While cruising, the system sends 90% of the power to the front wheels and 10% to the rear wheels. Acceleration puts more torque on the rear wheels. The car can put up to 70% of the total available power to the rear wheels to assist with rapid acceleration, and of that 70%, 100% can be pushed to either the left or right wheel in order to assist the vehicle through a corner.
The brakes on the new TL have been increased in size, from the older 11.8 in (300 mm) front disc and 11.1 in (280 mm) rear disc to the now Ridgeline-sized 12.6 in (320 mm) front discs and 13.2 in (340 mm) rear disc, still incorporating an internal rear drum e-brake while maintaining hydraulic discs for the foot applied brakes. The bolt pattern on the car is no longer a 5 mm × 114.3 mm (0.20 in × 4.50 in) but a 5 mm × 120 mm (0.20 in × 4.72 in) for this generation.
The SH-AWD model also includes some interior refinements over the base model and is tuned for slightly firmer suspension and steering feedback. It is visually distinguishable from the base model on the exterior by its SH-AWD badge on the trunk, quad exhaust pipes (as opposed to dual exhaust on the base model) and larger air ducts in the front bumper to cool the larger brakes (the base model's turn signal indicators in the bumper extend all the way to the center.) The TL rides on 245/50R17 tires, while the TL SH-AWD has 245/45R18 tires with optional 245/40ZR19 summer performance tires. Both models use electric power steering rather than hydraulic, and a revised five-speed automatic transmission featuring shift paddles on the steering wheel is standard equipment for both models. Acura has announced that a manual transmission will be offered in the 2010 SH-AWD model.
The fourth generation Acura TL adds further electronic convenience items, now including a central multifunction display, an eight-speaker 276-watt audio system with a six-disc CD changer, XM Satellite Radio, USB port connectivity (including full iPod control support), and Bluetooth Audio (for streaming music from a cell phone). Both models offer an optional Technology Package, which includes premium Milano leather seats, keyless start, a joystick-based (no longer touchscreen) navigation system updated with a new 8-inch (200 mm) full VGA display and the ability to provide weather information and traffic-based rerouting, and the Acura/ELS audio system with 10 speakers, 440 watts of power, DTS CD compatibility for 5.1 surround sound, DVD-A, as well as an internal hard drive with 13 GB of storage dedicated for audio. With the ELS audio system, audio CDs are automatically ripped to the hard drive upon insertion for future playback. The navigation system also stores its map data on the hard drive (as opposed to the previous model's DVD-based storage), producing faster boot times.