Automakers have suffered renewed disruption to sales because of changes in the European Union's vehicle type approval regulations.
Some brands such as Volkswagen, Audi and Nissan may not be fully ready for the introduction of the new tests, according to a study by Automotive News Europe sister publication Automobilwoche.
Starting September 1, all new passenger cars sold in Europe must be re-certified according to updated parameters for the Worldwide harmonized Light vehicle Test Procedure (WLTP), which was introduced a year ago to replace the previous New European Driving Cycle (NEDC).
Most brands are on schedule with the certification of their vehicles but VW said that it still had work to do.
"With very few exceptions, all engine-transmission combinations will [be certified] under the new emissions norm Euro 6d-TEMP EVAP-ISC,” Volkswagen said in a statement. "The remaining ones will then follow in the subsequent weeks."
VW's commercial vehicle division is less prepared, admitting that only 33 percent of its engine-transmission variants had been certified at the start of this month.
"There will be temporary restrictions," a spokesman said.
These are expected to include the VW Crafter, which will not be available in all configurations until 2020.
VW was hit the hardest by the shift to WLTP rules last year because much of its certification capacity was being used in the last couple of years to help it deal with the regulatory aftermath of its diesel-emissions cheating scandal, causing delivery bottlenecks and a big hit to sales.
Dealers have been hurt this year by delays in getting new vehicles.
"We have been feeling the distortions it caused for months. Important volume models could not be offered or were only [available] in very limited supply," said Timm Moll, head of the Moll Group, which specializes in the sale of VW Group models. "Customers that migrated to other brands as a result have been lost for years to come."
At the start of this year, VW said it could not rule out temporary bottlenecks in supply during the second half of 2019.
VW said it incurred costs of about 1 billion euros last year in connection with a limited offering and higher incentives to sell cars that could not be certified for sale in time for the initial introduction of WLTP last September.
Industry observers do not foresee the same level of disruption that hit automakers in 2018.
"We do not expect to see any major disruptions in the coming months ... and the new regulation will be far less disruptive than WLTP in September last year," Arndt Ellinghorst from Evercore ISI analysts said in a note to investors.