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Sigma is General Motors' mid-size rear-wheel drive automobile platform. The architecture debuted in 2002 with the 2003 Cadillac CTS and is adaptable for all-wheel drive and extended wheelbase versions. Development of the Sigma platform began at Holden in Australia before 1998 as GWRD or Global World Rear Drive.

The long-wheelbase Cadillac STS replaced the front-wheel drive GM K platform Cadillac Seville. The CTS was a replacement for the rear-wheel drive Cadillac Catera.

The Sigma platform has a four-wheel independent suspension with control arms in front and multi-link in the rear. GM's High Feature V6 and Northstar V8 are most common, though the small-block V8 has also been used. GM's 5-speed 5L40/5L50 automatic transmission is used throughout the range.

All Sigma vehicles are built at the purpose-built Lansing Grand River factory in Lansing, Michigan.

Vehicles based on this platform:

• Cadillac CTS 2003 - 2007
• Cadillac SRX 2004 - present
• Cadillac STS 2005 - present

[edit] Sigma II

Sigma II will debut with the 2008 CTS which will be larger and wider than its current counterpart it will share more parts with the larger Sigma I than the smaller Sigma I. Sigma II will be more flexible and will feature the new Direct Injection 3.6 HF V6 as its primary engine, the 2.8 HF may receive DI and would likely power the European Sigma cars. Sigma will stay a Cadillac exclusive.

The 2008 CTS will be the first model to ride on Sigma II, an improved version of the Sigma platform. It will be larger than the current model, and use the current 3.6 L HF V6 and a new more powerful 3.6 L DI HF V6, as well as supercharged smallblock V8 for the V-Series CTS. It will debut at the North American International Auto Show. Coupe and Wagon versions could arrive as 2009 model years.

Vehicles using this platform:

• 2008 CTS