VW tweaked TDI cheat in 2014 to reduce warranty claims

Some drivers may have unknowingly experienced \'test mode\' while driving.

Some owners of Volkswagen's cheating TDI fleet may have unknowingly experienced how the engines might perform after being brought back into compliance with emissions regulations.

In a criminal plea agreement with federal proseuctors, former VW engineer James Liang admitted that his team tweaked the 'defeat' system in 2014 after the company noticed an increase in warranty claims for parts and components related to emissions control systems.

"Some of Liang's coconspirators believed that the increased claims were a result of the vehicle operating in testing mode too long, rather than switching to 'road mode,'" the agreement notes. "Because of these increased claims, Liang worked with his coconspirators to enhance the defeat device to allow the vehicle to more easily recognize when the vehicle was no longer in testing mode."

The company rolled out the software revisions without revealing the actual changes. The deception was later repeated when investigators first raised concerns over emissions discrepancies, prompting VW to downplay the findings and offer revised software. The changes did not bring the vehicles into compliance, though many owners complained of poor fuel economy.

It is unclear if drivers may have noticed changes in performance if their vehicle was stuck in test mode. Full details of the defeat device algorithms have not yet been made public.

Liang's cooperation with investigators could result in additional enforcement actions against other VW workers, potentially shedding more light on the scandal as VW stalls disclosure of its own internal investigation.