[7] Cars were assembled at the Fiat Group factory in Pomigliano d'Arco, Italy and at a General Motors facility in Rayong, Thailand.

Until January 2002, the range-topping engine was the venerable 2.5-litre 24-valve Busso V6 - now with double overhead camshafts and four-valve heads - rated at 190 PS (140 kW).

Initially the 156 range was available with different options (packs) like a sport pack that included Blitz clothing, Momo leather interior and Recaro seats, it also included 16-inch (410 mm) wheels, lowered suspension and leather-trimmed steering wheel and gear knob.

A significant addition to the 156 range came in 2000 with the introduction of the Sportwagon station wagon or estate bodystyle, debuting at the Geneva Motor Show.

The 156 Sportwagon features fold-down rear seats to increase the luggage area normally covered by a privacy screen.

Also, the Selespeed gearbox control system was updated, buttons on the steering wheel were replaced by paddle shifters, as seen on the earlier Alfa Romeo 147.

In the center console, the designers added a multifunctional display with trip computer, fault, and service monitor.

Additionally, an MSR (Motor Schleppmoment Regelung) was added to the car, this device prevents wheel skidding by restoring torque to the engine for example when the gear is shifted down abruptly under conditions of low grip.

The only notable difference exterior-wise was body-coloured mirrors and bumper strips which were earlier black.

Late 2003 saw the launch of a facelifted 156, with new front and rear fascias designed by Giorgetto Giugiaro.

[19] A new top-of-the-line model was added to the line up called TI (Turismo Internazionale) designating a sporty kit, this version was equipped with modified suspension, bigger wheels (215/45 17") and leather-trimmed interior.

[21] 1,973 berlinas and 1,678 Sportwagons were built until the GTA production stopped in October 2005, as the V6 engine as unable to meet emissions regulations and due to the 156 being replaced by the 159.

The very first GTA was sold via online auction, from 13 to 23 September, the duration of the Frankfurt Motor Show.

The Q4 (short for Quadrifoglio 4) system used three differentials, the central one being of the Torsen C limited slip type; it added about 150 kg (331 lb) to the vehicle weight.

Other than the ride height, special 5-spoke 17-inch wheels and a "Q4" badge on the tail set the Sportwagon Q4 apart from the front-wheel drive 156 versions.

The Crosswagon's ride height was raised further compared to the Sportwagon Q4, giving the car better approach and departure angles; at 1,497 mm (58.9 in)[27] it was 6.5 cm (2.6 in) taller than a standard 156.

The Crosswagon was made to look more like an all-terrain vehicle by unique front and rear bumpers and door sills with steel inserts.

[28] The car had widened wheel arches, 19 inch tyres and was equipped with N.Technology limited slip differential.

At the 2004 Geneva Motor Show Italian-based tuning firm Autodelta unveiled a 156 Sportwagon prototype equipped with a 3,548 cc (3.5 L; 216.5 cu in) V6 engine that developed 300 PS (221 kW) at 6,800 rpm.

[29] The car was fitted with Bilstein adjustable shock absorbers, Eibach springs and Brembo front brakes with a diameter of 330 millimetres (13 in).

[30] London-based tuning firm Autodelta made two high performance versions based on the 156 GTA: in the GTA AM version, the Alfa Romeo V6 engine was bored to 3,750 cc (3.8 L; 228.8 cu in), making it capable of 328 PS (241 kW) at 7,300 rpm.

With this, the car could attain a top speed of 282 km/h (175.2 mph) and accelerate to 100 km/h in 5.2 s.[31] The GTA AM Super was an upgrade of the first version, now fitted with a Rotrex supercharger and rated at 400 PS (294 kW).

The 156 GTA only shared common parts with other 156 variants with respect to the facelift interior, doors, bonnet and boot lid.

[41] The Alfa 156 sedan and the station wagon were widely used by the Italian and other police and other law enforcement forces.