When engine manufacturers introduce even more stringent emissions-control technology on their 2010 engines they also will be adding sophisticated new onboard diagnostic systems.

The driving force behind the new diagnostics is the same one behind the new engines government mandates.

The U.S. Environmental Protection Agency wants to be sure that when the 2010 engines hit the road they will keep emissions low during the course of their useful life.

And the way to assure that is to require the adoption of certified onboard diagnostic systems for the engines and their fuel and aftertreatment systems.

With onboard diagnostic systems, a computer will alert the driver when any problem arises, electrical or mechanical, that could impact emissions levels.

For example, a motorcoach with a 2010 engine that develops a cracked particulate filter would be able to detect the problem before emissions rise above the regulated level.

The California Air Resources Board originally created onboard diagnostic system rules for passenger vehicles and now they will be adopted by diesel engine manufacturers for over-the-road buses and trucks.

The systems to be monitored by the onboard diagnostics include the crankcase vent, fuel, exhaust gas recirculation, boost-pressure control, particulate filter, cooling, and NOx reduction catalyst. Requirements for the systems include:

All diagnostics should run at least once per drive cycle, typically defined as engine start, engine running and engine off.

The system must have an operator interface, called a malfunction indicator lamp, that exclusively indicates emissions faults.

Service information must be adequate to guide a technician to the condition causing the problem and must be available to any service provider at reasonable cost.

Engine makers generally agree that while onboard diagnostic systems will assure emissions compliance, it also will make troubleshooting complicated.