Government regulators said Friday that they planned to step up the testing requirements of cars in the wake of the Volkswagen scandal.

The Environmental Protection Agency, which disclosed last week that it had learned that Volkswagen diesel cars had equipment to evade smog-testing standards, said it had sent a letter to manufacturers of gasoline and diesel cars saying that regulators would be looking for so-called defeat devices in all vehicles.

The agency said Volkswagen had used a device programmed to fool emissions testers into thinking that the car was emitting much less pollution than it was during regular driving.

“Manufacturers should expect that this additional testing may add time to the confirmatory test process,” the E.P.A. wrote in its brief letter. The agency said that the new procedures would start immediately and that the California Air Resources Board and Canada’s environmental regulators were involved with the more stringent requirements.