BEIJING – Carmakers have to be more transparent about the way they certify their fuel economy and emission ratings as regulators step up scrutiny into the gap between laboratory results and real-world driving conditions, according to Daimler AG Chief Executive Officer Dieter Zetsche.

“You can only be transparent and if there’s any shortfalls anywhere, fix them and move forward,” Zetsche told Bloomberg News ahead of the Beijing auto show opening this week in the world’s biggest vehicle market. “And then, of course, it will take some time” for the auto industry in general to be where they were before (the) Frankfurt motor show last year.”

Revelations about Volkswagen AG’s cheating on diesel emissions emerged after the Frankfurt motor show in September. Since then, government fraud investigators have raided French manufacturer PSA Group as part of broader checks into vehicle emissions. In Japan, Mitsubishi Motors Corp. last week admitted that it manipulated fuel-economy tests to mislead consumers.

Daimler said last week it had been asked by the U.S. Department of Justice to investigate the certification process of its cars. The internal probe follows U.S. class action suits that allege some of its cars violated emissions standards. Daimler has said it’s cooperating fully with authorities and that the suits are “baseless.”

The suits against Daimler say Mercedes-Benz clean-diesel models contain a device that causes the vehicles to violate U.S. emissions standards when run at cooler temperatures, making them less environmentally friendly than advertised. Specifically, the automaker was accused of using a device in its BlueTec cars to turn off a system meant to reduce polluting nitrogen oxides in its exhaust.

The U.S. Environmental Protection Agency also contacted Daimler earlier this year over the allegations, which Zetsche rejected in February as without merit. While Daimler has acknowledged the existence of a device, it says it’s legal and designed to protect the engine.

Zetsche said that Daimler is “very active” in helping European authorities enhance and accelerate the definition of new testing cycles that give a close comparison between test and reality for fuel consumption.

“The same applies for the emissions,” he said. “We think that is one important element that you get more similarity there and the general public can understand better than today because there is less difference between what you measure outside and what you measure in the lab.”