GM Service Manual Online
For 1990-2009 cars only

Your vehicle's V8 engine may have Displacement on Demandâ„¢ (DoDâ„¢). This system allows the engine to operate on either all or half of its cylinders, depending on your driving conditions.

When less power is required, such as cruising at a constant vehicle speed, the system will operate in the half cylinder mode, allowing your vehicle to achieve better fuel economy. When greater power demands are required, such as accelerating from a stop, passing, or merging onto a freeway, the system will maintain full-cylinder operation.