IATF 16949 is not an ISO standard
It is an automotive certification scheme with its own rules. A general vehicle workshop, fleet operator or dealership is not automatically an IATF candidate; a direct OEM or automotive supply chain customer requirement is needed.
CE marking is not an ISO certificate
CE and EN 1090 are product and market conformity, not a management system certificate. The two operate under separate rule sets.
ISO 3834 is not a management system standard
It sets product and process quality requirements for welded manufacturing. The customer standard and the welding process are questioned separately.