The European Union has moved to change its diesel car emission tests to prevent the sort of rigging used by German car giant Volkswagen after noticing discrepancies in the results, EU sources say.
The sources, who asked not be identified, said research over several years showed a difference between emission levels recorded in the laboratory and those found in real-world driving conditions.
"The lessons we took from that very quickly is that we needed to commence new, more reliable road driving emissions testing, which should also prevent any kind of a defeat device being installed," one source said of the moves to tighten tests that come into force in early 2016.
VW sparked global outrage after the iconic company admitted that 11 million of its diesel cars were equipped with so-called defeat devices that covertly turn off pollution controls when the car is being driven and turn them back on when tests are being conducted.
The scandal broke in the United States, where VW faces possible fines of more than US$18 billion (NZ$28.17 billion), but diesel cars account for only a small part of the market there.
In Europe, they are mainstream and have been marketed as more fuel-efficient and environmentally friendly than traditional petrol-engined cars.
News that EU officials had noticed emission discrepancies between on-road and testing situations was first reported on Saturday by the Financial Times, which said little was done to address the issue after it was discovered in 2013.
European authorities rejected that claim.
Asked if the Commission knew that defeat devices existed, one of the EU sources said: "Yes, we banned them. Did we know defeat devices were being used in the EU? No."
Another source added the reinforced testing that has been in preparation since then has been developed to thwart such cheat technology.
The European Commission, the EU's executive arm, said on Friday that "currently emissions are measured on a laboratory test cycle (NED) which does not reflect the emissions of vehicles in normal driving conditions."
"To address this shortcoming, the Commission has been working to develop Real Driving Emission (RED) test procedures," it said.
The new testing procedure will come into force in January, the Commission added.