NEW YORK (CNN/Money) - Federal auto safety regulators proposed new rules Wednesday requiring automakers to include a system to gauge tire pressure on all new cars.

Under the proposal from the National Highway Traffic Safety Administration, the system must be able to detect when any of the vehicle's four tires is more than 25 percent underinflated, and it must alert the driver to the problem by lighting a dashboard warning light.

The system must also warn the driver when the system itself is not functioning properly, under the proposal.

The spare tire would not have to be monitored, and NHTSA points out in its announcement that the system would not be a substitute for drivers regularly monitoring tire pressure. Low tire pressure can cause increased tread wear and blow-outs as well as increased fuel consumption.

The systems would add about $115 to the retail cost of a new car, according to the Alliance of Automobile Manufacturers, an auto industry lobbying group. The systems would also save money, however, through decreased maintenance costs, according to NHTSA.

The new rule would apply to all passenger vehicles weighing 10,000 pounds or less. The requirement would begin with the 2006 model year, starting Sept. 1, 2005. Half of all vehicles manufactured, starting on that date, would have to comply with the rule. In the second year, 90 percent of vehicles would have to comply, and after Sept. 1, 2007, all vehicles would need to have the monitors.

The agency was mandated to create an automatic tire pressure monitoring requirement by the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) act. That law, which also deals with vehicle recalls and defect reporting, was passed by Congress in 2000, after a rash of crash deaths that occurred when Ford Explorer SUVs rolled over. Those rollovers were caused by the failure of factory-installed Firestone tires on the vehicles.

NHTSA will accept public comment on the proposed rule for the next 60 days.