WASHINGTON Diesel engine manufacturers and the trucking industry are urging the U.S. Environmental Protection Agency to step in and harmonize pending federal and California onboard diagnostics rules.

The two groups believe that 'without (EPA) leadership, disharmonized (onboard diagnostic) requirements could adversely lead to the California standard becoming a de facto national standard, should California requirements be more stringent than federal standards.'

Late last year, the EPA proposed a regulation that would require diesel engine manufacturers to phase in devices that would constantly monitor the performance of their reduced-emissions engines, starting in 2010. Beginning in 2013, all over-the-road bus and truck engines would have to meet the requirements.

Meanwhile, California developed its own proposed onboard diagnostic rule. Both the federal rule and the California version would require over-the-road trucks and buses to be equipped with onboard diagnostic systems that exceed what manufacturers currently provide.

Under the Clean Air Act, California can enforce its own emission regulations if it receives a federal waiver, and other states have the right to choose Californias emission standards over federal standards.

The proposed California and U.S. regulations are similar, 'but the CARB regulation is more stringent, with tougher failure thresholds' for the devices, said a spokesman for the California Air Resources Board. 'If there is a problem with an emissions control system, the CARB standard would require that the OBD system detect the issue sooner than the federal standard would.'

The Engine Manufacturers Association says if California is allowed to proceed on its own, before EPA finalizes its nationwide rule, 'states may perceive that there is a need for them to opt in to the California rule.'

'A state-by-state opt-in . . . could have disastrous consequences for the heavy-duty engine and vehicle industry . . . as it would, among other things, require manufacturers to label, distribute and track engine products meeting California requirements in some states and federal requirements in others,' the association of engine makers said.

'EPA can, and must, do what is necessary to minimize such an adverse result,' the association added.

But CARB contends that its onboard diagnostic regulation gives manufacturers sufficient lead time to develop and implement new onboard diagnostic systems, allowing them to gain experience 'on a smaller number of engines prior to wide-scale implementation.'

Thats not good enough for truckers. 'We want to make sure that (California and federal) onboard diagnostics proposals are consistent with each other,' said an environmental affairs official with the American Trucking Associations.

'We want the same requirements for manufacturers' across the nation, "so they can produce a single U.S. truck, and not have to comply with two different standards.'