BEIJING, March 6 -- When Sun Yongli bought his sleek Mercedes Benz C200 five years ago, he never expected the limo would give him such a headache.

The 33-year-old, who works for an Internet company in Shenzhen, told Xinhua that he chose the model partly due to the brand's reputation for safety, but Sun believes the smell of the vehicle's interior may have hurt his health.

He is among many Chinese affected by the same issue, with suspicions that the whiff indicates the presence of noxious chemicals. Now, ahead of the International Day for Protecting Consumers' Rights on March 15, pressure is being placed on the vehicle's manufacturers to do something about the issue.

Sun says the typical "new car smell" went away about a year after he bought the Mercedes in 2009, but another "melted crayon smell" became more and more conspicuous since 2011.

"I often felt dizzy and nauseous after driving for a little while," Sun claims. Besides short-term effects, he has found his immune system may have been damaged. "Since 2010, my physical examination results showed abnormally high levels of white blood cells and lymph indicators."

His C200 is a member of the Mercedes Benz C-class series of compact cars. It was produced by Beijing Benz Automotive Co., a joint venture by BAIC Motor Co., Daimler AG and Daimler Greater China Ltd.

The C-class vehicles, especially domestically manufactured ones, have been frequent targets of complaint in China for their smell.

On QQ Group, a group discussion function on popular instant-messager QQ, a search for "Benz," "peculiar smell" and "safeguarding legitimate rights" returns 33 groups attracting more than 2,000 users.

Their most common claimed symptoms include dizziness, headache, nausea, decreasing immunity and problems with eyes and respiratory organs.

"The Benz is poisonous. I have to open the windows when I'm driving it," according to a QQ user with the screen name "Sanloulouzhang," who like Sun owns a 2008-model C200.

His solution -- opening the window -- was also taken by most other owners in a QQ group interviewed by Xinhua. Of course, they have tried other more substantive measures too.

In mid 2012, Sun reported the smell to his after-service 4S store, which blamed the car's carpet and agreed to replace the offending floor covering free of charge.