Renault is planning a software upgrade to cut nitrogen oxide (NOx) pollution from its diesel engines, which have come under fire for their relatively high emissions in the wake of the Volkswagen test-rigging scandal.
Following VW's exposure last September for using software "defeat devices" to cheat US regulatory tests, the French carmaker has drawn public and investor scrutiny over its own emissions performance.
As of Monday's market close, Renault shares had fallen 14 percent since the January 14 disclosure that investigators raided its offices this month over suspicions of emissions fraud - since roundly denied by company and government officials.
Besides VW's outright cheating, the diesel scandal has heightened awareness of real-world NOx emissions by the broader car industry, far exceeding those measured in flawed European regulatory tests - with Renault often cited by campaigners as among the worst offenders.
German green group DUH said in November that Renault's popular Espace minivan had released NOx emissions 25 times over EU limits during a Swiss study using driving styles that are more realistic than the EU test cycle.
"We agree that our position is not satisfactory," Renault Chief Competitive Officer Thierry Bollore told reporters at the company's headquarters west of Paris, while disputing many of the reported measurements.
"We are the first ones to admit that we have room for improvement."
Testing by a French government-led commission established after the VW scandal has also found relatively high NOx emissions from Renault models, members have said.
The French carmaker will detail the planned adjustments in March for vehicles with the latest Euro 6 generation of diesels, Bollore told reporters on Tuesday, and begin offering voluntary engine checks to owners four months later.