Liebe Unterstützer!
Zunächst meinen herzlichsten Dank an alle die so eifrig mitgedacht und unterstützt haben.
So viele schnelle und qualifizierte Antworten habe ich in keinem Forum bekommen.

Das Problem wurde nun auf der AS/400 Seite gelöst. Ich bin weit davon entfernt zu verstehen, was da genau gemacht wurde. Vielleicht kann der eine oder andere aber damit etwas anfangen.

Vielen Dank nochmal an Alle!

This morning my colleague finally found out what the problem was causing the Iserie system to get into a loop for special characters like ü . It was related to a security tool Robot/Security are using to secure are system. This tool starts jobs when a Iserie server is started for an ODBC connection

Below actions was taken to solve the problem
For an number of servers an RSE (Robot/Security) program was defined as exit program, this was also setup for the “Database Server – entry” (QIBM_QZDA_INIT).

When an SQL statement makes a where selection with the Umlaut (when CPU use goes up) a number of RSE programs are on top in the program stack of the related job QZDASOINIT.

All defined RSE exit programs for exit point are removed. The prestart jobs QZDASOINIT are stopped and restarted..

We can conclude that the problem was not caused by a wrong code page or the ODBC driver.

Thanks for all the support you gave me last week to solve this issue. The cause of this problem was also a complete mystery to me.