Daughter board communication error

[Piv]

Hello, I've been doing some research before creating a new post and found some good info but all the threads are closed and my problem still here

The car is a golf mark1 with a K20Z in it, K20A JDM loom and PRC ECU with a Kpro3

I've been able to remap the car few months back with this error code coming on only the first time I started the car due to a loose ECU ground connection on the inlet manifold, fix this and the car's been fine during the whole mapping session

The customer then called back after few weeks to tell us he had this error code coming up all the time

The car is now back with me and I tried many things, including new ground, recheck alternator wiring, battery voltage etc...

I've done a log when the car start and while the car's running if I clear the error code, it does come back up even if the battery voltage doesn't drop at all

Any ideas ?

Thank you,

Piv

[Spunkster]

What is the battery voltage at the ECU when starting, measured with a multimeter?