"The class action alleged Hilux, Fortuner and Prado vehicles sold between October 2015 and April 2020 had defective diesel particulate filter systems, leaving owners out of pocket. The defect caused the vehicles to spill foul-smelling white smoke and decreased fuel efficiency."
"Toyota redesigned the DPF to fix the issue, rolling it out in a 2020 update, while Toyota New Zealand is confident it has rectified the issue for all affected vehicles here, replacing the DPFs, or even the entire vehicle in a few cases."
My understanding of this issue was as follows.
Diesel particulate filter (DPF systems capture carbon particles from the exhaust stream. Those particles slowly clog up the filter, but can the particles can be burnt off at high temperature (carbon + oxygen goes to C02). Variety of approaches to do the burn off, But typically the vehicle runs a cycle designed to increase exhaust heat.
For whatever reason, many Toyota's (Hilux, fortuner & Prado's) manufactured from 2015, struggled with their DPF cleaning cycles, leading the the vehicle repeatedly trying (Burning heaps of extra fuel to try increase exhaust temperature, and puffing out white smoke. If the vehicle was unable to ultimately clean it's own DPF, it would requre being taken to a workshop.
Toyota (and many owners groups) knew about this issue for a long time, but did not resolve it until 2020.