No electronic sensor failure on my Optima. Only the Check Engine Light came on for faulty O2 sensor/front catalytic converter (P0420 code). Replaced the front cat con to SS extractor for performance instead.

Repairs I've done over a year of owning the car:
1. Change projector housing and HID to led. Projector housing coating started to corrode/oxidise until 1 side doesn't reflect the light properly. Cost RM 1k total.
2. Change new compressor, condensor, cooling coil and actuator valve. Aircon hot when idle, cold when rev, should be same issue with Cerato. Cost RM 2.8k total.
3. Change suspension parts due to wear and tear. Stabilizer link, bushing, link arm, steering yoke, absorber mounting. Cost RM 800 total.
4. Change spark plugs bcos 1 cylinder misfiring. Cost RM200 total.

I would say electronics failure is very rare for the cerato and optima, its either mechanical or wear and tear parts. I would standby RM 5k for repairs once you get the car just in case.

My friend's elantra bought 2nd hand in 2019 (2015 model 1.8) -> change suspension parts due to wear and tear, steering wheel clock spring.
My friend's cerato bought 2nd hand in 2020 (2015 model 2.0) -> change absorbers and control arms due to wear and tear.

There are reliable workshops around that specializes in Korean cars and frequented by FB Kia group members.
Penang has 1, Johor has 1, KL have a few.