Here's why the EPA is so concerned about urea: The emissions system on virtually all of today's cars is engineered to be maintenance-free. Unless a part fails, the driver doesn't have to do anything to keep the emissions system working. But a diesel-powered car with a urea-injection system requires the driver to take an active role in ensuring the car continues to meet emissions standards.
If the vehicle runs out of urea, it falls out of emissions compliance.
Karl Simon, the EPA's acting assistant office director for the Office of Transportation and Air Quality, said it's up to automakers to present such a warning system to the EPA for approval. He said the EPA is not crafting any rules or guidelines on how automakers should engineer the warning system, but it would offer guidance if asked.
Simon also said that the agency must be satisfied that urea can be easily obtained. The EPA wants drivers to have ready access to the chemical.
Mercedes-Benz plans to launch several vehicles with clean diesel engines and urea-injection systems in North America, possibly as early as 2008. Chrysler's 300 sedan and Jeep Grand Cherokee also could get the Mercedes-designed urea system. Several other automakers, including Ford Motor Co. and General Motors, have studied SCR technology. The EPA says more than one automaker has approached the agency about using urea.
Mercedes' Boxfish bionic concept car is equipped with a prototype of the production urea system Mercedes likely will use around 2008. The vehicle has the urea tank located in the spare wheel well.
Mercedes wants to make the urea system invisible to the driver. The tank would be replenished when the car is brought in for regular maintenance, between about 10,000 and 12,500 miles.
The EPA wants urea-equipped vehicles to have some type of early warning system. The system would not only alert drivers when the urea tank is low but also motivate them to take their vehicles back to the dealer for a refill before the fluid runs dry.