Shares in French car manufacturer Renault have fallen 20% after police raids on several of its factories.
The company confirmed the raids, saying that fraud investigators wanted to check equipment at its factories.
Investors feared that Renault was being investigated for cheating exhaust emissions tests, which Volkswagen admitted to doing last September.
However, Renault stressed that tests have shown “no evidence” of devices designed to cheat emissions tests.
It said the fraud investigators were looking at the way Renault uses exhaust emissions technology, and it was fully co-operating with the probe.
Police have not confirmed why the raids were carried out.
Renault shares later recovered some of the early losses, to trade almost 9% lower.
News of the searches first came from the CGT Renault union. It said the raids targeted the engine control units and that they were likely to be “linked to the consequences of the Volkswagen rigged-engines affair”.
The union also said police officers took the personal computers of several directors.
Last month, Renault said it would invest €50m (£38m) into bringing the real emissions of its cars into line with those measured in official test conditions.
Authorities and car manufacturers have been on alert in the wake of the Volkswagen emissions scandal, which emerged in late September.
Volkswagen (VW) admitted its diesel-engine cars had been fitted with computer software designed to flatter emissions data during tests.
In the days following the scandal several car manufacturers issued statements affirming their cars adhered to all emissions standards and were not fitted with cheat software.
VW said around 500,000 cars in the US had been fitted with the devices, which were designed to make VW cars appear more fuel efficient and environmentally friendly than they really were.
It also announced plans to recall and inspect 8.5 million cars in Europe, including 2.4 million in Germany, 1.2 million in the UK and 500,000 in the US.
Meanwhile, Renault’s French rival Peugeot said its factories were not involved in the raids. The company also pointed out that its car emissions equipment had passed recent tests to ensure they complied with regulations.
“The test results carried out by the technical committee of Energy Minister Madame Royal were passed on to us and the showed an absence of anomalies,” a Peugeot statement said.