The damning claims come from a report submitted by the Volkswagen Diesel Customer Forum (VDCF) that says owners of cars issued with a fix for affected 2.0-litre diesel engines have also noticed increased exhaust smoke, excessive regeneration of diesel particulate filters (DPF) and DPF failure.
It says exhaust gas regeneration (EGR) valves have also failed, as have turbochargers and fuel injectors. Further claims state that other vehicles have entered limp mode or their engines have got louder once the voluntary fix was issued.
But VW has told Autocar that these issues affect less than 1% of the 600,000 cars it has fixed (at around 20,000 a week), which equates to less than 6000 cars overall.
A spokesman said: "That means that over 99% of customers are satisfied with the application of the technical measures, which of course are carried out free of charge. As you would expect, we make it a priority to look at the vehicles of the very small proportion of customers who report any issues."
VW also believes that a large portion of the vehicles with problems have been poorly maintained, with some even missing their factory-fitted DPFs. It says this means many of the issues that have arisen are unrelated to the fix.
VW has repeatedly claimed that its emissions fix, which is focused around a software change in affected models, has no impact on vehicle performance and that it has been “extensively tested” and approved by “relevant independent authorities”. The company said it tested 200,000 vehicles in the software’s development.