Since i bought my gsr,i was told by a GENIUS cordia technition,(Alltime you Know who Im talking about) that my speed sensor which is located on the gearbox Doesnt work.So what does this componant do when you drive -Does it add more fuel to engine or what does the computer interprete from the Thing.At high rpm/speed does it do sumthing to the EFI.Looking at the wiring diagram its got a black wire to earth,Than a yellow white wire to the computer A-15.

As far as I know it is a speed switch, so it is either on or off. It increases the idle when you start rolling so it dosen't bog down the engine when you let the clutch out. Can't think of any other uses for it, although there may be some, but nothing too important like mixture/ignition/high speed.

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'88 Eterna ZR4
'86 Cordia GSR

it stops fifth engaging at standstill too

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Gallo 24 all the way

The speed sensor is a reed switch located on the back of the speedo.
The ecu uses it to help decide what it wants to do with the isc. My
Mitsubishi manual says that it is used by the 5th gear control relay
to prevent shifting into 5th gear below 10kph.