Speedometer reading 35 km/h while at a standstill, 55 km/h anything above 20 km/h

[V35 owning idiot]

I got my V35 back in November 2020, I am the 3rd Australian owner to my knowledge. I have spent the past year and a bit trying to fix all the things the previous owners have broken, much to no avail. It had 1 little gremlin I could never fix, The speedometer would occasionally default to 35 km/h and then go to 55 km/h when I started moving. It would normally only do it for 22 to 40 ish minutes, Its been doing it for now 5 straight days. Does anyone know what could possibly be the reason, I've tried taking the dash out, re-soldering the terminals, doing an ECU reset, everything but it still keeps happening. Its a 2003 5AT V35 coupe 350GT. (Note the trip meter is still getting correct knowledge of distance, it only goes up when moving and the slip light is not on) I currently have the dash out and trying everything I can, I know the most logical answer is buying a new dash but I would rather not have to. 

[SomeFReaK]

I pulled apart a cluster to work out how the fuel level, indicators and other warning lights work. It seems to use can-bus to communicate alot of the information to the dash, the onboard IC's then control a bunch of things. From memory speed is one (along with tach, temp, CEL, SLIP, and more). IMHO The most likely cause is probably a fault in the cluster. 

[V35 owning idiot]

I used a multimetre to do some poking around in there and there is a stray 0.6 volts when the key is turned to the 'On' position and increases to 0.8 volts before dropping volts back to 0.4 volts. Thank you for your time

 

Edited July 17, 2022 by V35 owning idiot