Mitochondrial intermembrane chaperone that participates in the import and insertion of multi-pass transmembrane proteins into the mitochondrial inner membrane. Also required for the transfer of beta-barrel precursors from the TOM complex to the sorting and assembly machinery (SAM complex) of the outer membrane. Acts as a chaperone-like protein that protects the hydrophobic precursors from aggregation and guide them through the mitochondrial intermembrane space. Compared to TIM10, it may have a strong structural role. Heterohexamer; composed of 3 copies of TIM9 and 3 copies of TIM10, named soluble 70 kDa complex. Associates with the TIM12 component of the TIM22 complex, whose core is composed of TIM18, TIM22 and TIM54. Interacts with the transmembrane regions of multi-pass transmembrane proteins in transit. The twin CX3C motif contains 4 conserved Cys residues that form 2 disulfide bonds in the mitochondrial intermembrane space. However, during the transit of TIM9 from cytoplasm into mitochondrion, the Cys residues probably coordinate zinc, thereby preventing folding and allowing its transfer across mitochondrial outer membrane (Probable). Belongs to the small Tim family.