The investigation, based on a 2003 VW Touran – fitted with the 1.6-litre diesel – discovered discrepancies between the before and after figures following the software update by Volkswagen.
Fuel economy on the Touran fell from 50.72mpg to 47.61mpg. At the same time, CO2 emissions rose from 147.3g/km to 156.9g/km. The harmful NOx emissions meanwhile, which were the target of the ‘cheat’ software, were halved after the fix was applied from 0.639g/km to 0.351g/km.
The tests were performed by Autocar at the Millbrook Proving Ground to a repeatable real-world test cycle using the most up-to-date international industry-standard equipment for testing vehicles.
The findings were disputed by VW however, who pointed out there were actually 20 variables that can potentially affect economy tests.
It also stressed the tech fix had no effect on a vehicle’s economy or performance.
A VW spokesman said: “It should also be noted that the relevant approval authorities have approved the technical measures and that during the development of the technical measures, “Volkswagen worked with care to ensure that fuel consumption figures in the homologation cycle and on the road remain the same when compared with the previous software.
“If increases in fuel consumption were detected during the development phase, the software was revised and retested.”
VW has been heavily criticised since the scandal first broke in 2015. The software updates and lawsuits fielded by the company are expected to have cost tens of billions.
So far, more than 600,000 of 1.2million VW models fitted with the affected EA189 model have had the recall completed.
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