CR: Turning Off Cheater Software Makes VW Diesels Slower, Less Efficient

Consumer Reports says its tests of diesel-powered Volkswagen AG cars indicates the software VW used to cheat emission standards also makes the vehicles peppier and more fuel efficient.

CR tested two cars: one with VW's now-discontinued EA 189 4-cylinder engine and one with the company's more sophisticated next-generation EA 288 4-cylinder design. VW concedes both engines were equipped with software that relaxed emission controls when the cars were not being tested for emissions.

CR claims it figured out how the cheater mode worked and was able to defeat it, thus forcing the engines' emission controls to function as intended under road conditions

The magazine says a 2011 model Jetta SportWagen, fitted with the older diesel and operating in cheater mode, accelerated from zero to 60 mph in 9.9 seconds and delivered fuel economy of 50 mpg. When the software was neutralized, thus forcing the engine to conform to emission standards, acceleration and highway fuel efficiency fell to 10.5 seconds and 46 mpg, respectively.

The differences were smaller in a 2015 model Jetta sedan powered by the company's newer diesel, CR says. With the cheater software active, the car achieved 60 mph in 9.1 seconds and fuel economy of 53 mpg. With the software deactivated, the car reached 60 mph in 9.2 seconds, and its highway fuel economy slipped to 50 mpg.