my nissan march 2002 gear suddenly shift to low gear. what is the main problem?

Question

My nissan march year 2002 1.4 sometime running in low gear. Sometime running in high gear but suddenly shifted to low gear.

Answer 1

I would start be replace the transmission fluid. it should be replaced every 30k or so.

if you find metal pieces in the fluid, the transmission will have to be replaced and the transmission lines will have to be flushed. its cheap are safer to install a used transmission.