Hello,

For pursuing mechanical engineering course the basic requirements is maths along with other two subjects physics and chemistry.

Without this no institutions is going to admit you.

And there is no facility of doing one subject in open learning or distance learning you have do your class 12 again to gain the certification.

Secondly you can give maths paper alone as a certificate course. You can give the mathematics paper from NIOS as these certificates are valid, recognized and at par with the other national and state boards of school eduction.

Or you can opt for another route that is diploma and the lateral entry into your mechanical branch.

https://nios.ac.in/student-information-section/on-demand-examination.aspx

Please refer to this link for more information.

Hope this helps!!!