All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad (ﷺ) is His Slave and Messenger.
There is no blame upon you for engaging in the work mentioned, so long as your role is limited to diagnosing faults, carrying out repairs, inspections, replacements, and handling warranties. This is because such work does not involve direct participation in what is unlawful, such as managing interest-based contracts, nor does it constitute assistance in them through promotion, facilitation, or any other form of aiding in what is unlawful.
The purpose of repairing cars is much broader than being limited to selling them through interest-based transactions.
Allah Knows best.