Mori Seiki ZT1500Y Turret Indexing Problems

Hi anyone out there with experience repairing Mori Seiki TM centers. I recently started working on the CNC turn Mill centers and have little experience doing repairs.

I have been having a problem where the lower turret will index properly but then the signal X15.5 will go from 1 to 0. A few seconds later I receive the "Turret Index Time Over #2" alarm and I must reset D150.1 back to 1. I can then index the turret a few more times until the same thing will happen.

The turret is not out of position when I do this and the signals X15.3 and X15.4 for clamped and unclamped are acting as they should. I contacted DMG Mori and they said that the signal X15.5 is for the "rotary sensor SQ117" which i have located under the maze of panels and covers that are on the lower turret.

Does anyone know what that sensor is supposed to be sensing?
What should I do now to try to debug the sensor?
Is it worth pulling the sensor out and checking it, or am I on the completely wrong track for this problem?

Thanks for the help in advance, I hope someone out there can help me. DMG Mori hasn't given me much useful information.

As a side not: If anyone could give me manuals and diagrams for the Mori Seiki ZT1500Y that would be great, all I have to go with is a short "Maintenance Manual" which mostly covers routine maintenance not repairs.