Wa Alaikum Salam.
Bro, well maintained, good condition 2010-2012 model Vitz will be hard to find, they will be badly and severely abused / misused. Those in good condition will cost too much.
On the other hand, well-maintained and mint condition Passo (if available) will cost quite reasonable in comparison to Vitz, and tbh, Passo is a decent, reasonable and family car.
You can get well-maintained, mint condition 2013 model Passo in 13-13.5 lac PKR, with auction grade 4.5 (or above).
I think, your mechanic knows little-to-no about Passo. Is this a luxury sedan? that it has many sensors?
It will be having the similar sensors as found in Vitz (but depending on trim), and has the same 1KR-FE engine and CVT transmission as found in similar model year Vitz.
I would sincerely advice to change your mechanic.