Over Voltage Protection device..

It basically is just a smart fuse and it's purpose is to protect the ECU form voltage spikes , preventing ECU damage.
They are known for causing ECU related faults as they interrupt feed power to ignition and fuel suppy.[ along with abs]
The late 124 chassis IL-6 had so much trouble with them, that they came out with a modified part, so any time one is seen with the original part # , it is recommended that it be changed before blaming part failure on ECU and other electrical parts before hand...

Do a search on OVP and you will have enough reding for a week...