the 4wd / attessa system copies a few signals from the main ecu and they get relayed to the ECU in the boot
so passenger foot weel = main car ecu
boot under parcel shelf = 4wd / abs / active lsd computer
the main signals are speed, rpm and TPS
TPS is probably the main one as at car bootup if TPS is not present (to the 4wd computer) it will fail and give up
also if TPS goes out of whack at runtime then it will give up the ghost. check and trace the TPS wire or make sure your TPS wire at the 4wd computer has voltage at idle should be around 0.33v ish give or take.