Possible reasons and things to look at? TIA.

4d56 turbodiesel.
reads 11+volts at glow plugs. parallel resistance for all GPs is 0.5 ohm.
glow plugs are kitahara pm75. never been replaced for 3 years.
the glow plug controller is located at the kick panel at driver's side. contains 10 pins if im not mistaken. any voltage reference chart for this controller?
temperature sender resistance test is ok. about 300 ohms at operating temp.