Nearly 1.6 million claimants are pursuing manufacturers, including Mercedes-Benz, Ford, Nissan, Renault, Peugeot and Citroën over allegations that their diesel vehicles were fitted with illegal "defeat devices" between 2012 and 2017.

Lawyers for the claimants told the High Court that these devices detected when cars were being tested and artificially reduced nitrogen oxide (NO) emissions to within legal thresholds. Once on the road, however, emissions reportedly soared to as much as 12 times the permitted levels.

The case comes a decade after Volkswagen's dieselgate scandal rocked the automotive industry. VW's admission in 2015 that it used defeat devices has already cost the company over R640 billion in refits, fines and legal settlements.

Tom de la Mare, representing the claimants, argued that car makers across the sector made a "conscious decision" to put customer convenience ahead of pollution control.

The manufacturers strongly dispute the allegations, insisting their emission control systems were legitimately calibrated to respond to different driving conditions. They reject any comparison with the VW scandal.

The trial will examine 20 sample vehicles from the five manufacturers named by approximately 850 000 claimants. A judgment is expected by mid-2026, and the ruling will also apply to roughly 800 000 additional claims against other brands, including Vauxhall/Opel and BMW.

Should the court find the sample vehicles contained prohibited defeat devices, a separate trial will determine compensation levels.

This marks the second time the High Court has adjudicated on defeat devices, having previously ruled against VW in 2020. VW settled without admitting liability in 2022.