Many motorists wonder what it actually means for a car to be considered “clean”. The new Jetta TDI is a prime example. This car will use a new fuel that is an ultra-low sulfur diesel. It used to be that diesel fuel contained large amounts of sulfur, which harmed devices like catalytic converters that are put in the exhaust stream to help clean harmful emissions.

Now, ultra-low sulfur diesel has reduced the content of sulfur by 97%, which allows carmakers to add devices that will reduce emissions, without risking damage to the components. Of course, devices like these will vary from carmaker to carmaker, just like new car warranties.

There are four new emission-reducing devices in the new Jetta TDI. According to VW, they are an oxidation catalyst for carbon monoxide and hydrocarbon emissions, storage catalyst for nitrogen emissions oxides, particulate emissions trap, and for hydrogen sulfide emissions, a slip catalyst.

Changes that have been made under the hood of the 2009 Jetta TDI include four valves per cylinder (not two), common rail fuel injection, and new calibration for the engine. However, like with any vehicle, it is important to have a good roadside assistance program.