It’s important to keep the following in mind when discussing Toyota manufacturing and abstract terms like “quality”…
Toyota, globally, is fully 100% rationalized in terms of how they do the work of manufacturing vehicles. Every plant operates the same, every process is very much the same— whether you are at the Toyota Turkey plant, Toyota Kentucky, Toyota Tahara, Toyota Honsha, etc. They are all mirror images of each other. Highly automated, highly robotic, and highly vertically integrated.
Now, there are differences in kind when it comes to Toyota Group companies that are outsourced for assembly… Toyota Auto Body is a good example of this.
TAB was formerly ARACO which was formerly Arakawa Auto Body, etc. These wholly owned subsidiary manufacturers are what most industrial engineers call “black box” suppliers. They are black boxes because they operate fully and wholly on their own without any interference from the mothership (in this case, Toyota Motor Corporation).
TAB is involved in design, prototyping, testing, manufacturing testing, QDR analysis, part engineering, and all processes of vehicle manufacture with little to no assistance from TMC. Toyota has embedded engineers and project managers at these “black box” suppliers, but the actuality is that a product like the Land Cruiser is designed and “framed” by Toyota engineers and then handed over to TAB engineers to finish of the truck. Mainly, important to keep in mind, the LC is an evolutionary platform. Not a revolutionary platform. Hence all changes are incremental over time.
A supplier/assembler like TAB is considered a “mature supplier”— IE: all of their systems, QA/QC protocols, processes and internal structure are mirrors of their “mother”— TMC.
The only time TMC will get involved with a supplier like TAB is during new model introductions for manufacturing and new model release, or if there are quality issues that need TMC intervention in the Gemba. Otherwise, it’s very much hands off.