BMW's boss has urged caution over proposed plans to share technology and resources with Daimler.
The two companies are reported to be considering platforms and sharing or merging their financial services operations.
But BMW's Norbert Reithofer told the Frankfurter Allgemeine Zeitung newspaper: ""There are clear limits. The BMW brand, which one study has valued at $24 billion (£15.8 billion), must not be diluted or the brand identity damaged."
Reithofer said that talks with Daimler were ongoing, and added that he would be willing to strengthen ties with its French engine partner, PSA/Peugeot-Citroen.
"When the new Peugeot chief is in office, we will also discuss whether one can expand the existing cooperation," Reithofer said.
Last week, Daimler bossDieter Zetsche called for a broader alliance with BMW, saying there were only a few areas where a co-operation was out of the question.