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.