As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PREDEPARTURE CHECK, THE LT ANTI-ICE VALVE FAILED TO OPEN. DURING TROUBLESHOOTING OF THE SYSTEM FOUND THE DIODE D25 HAD HIGH RESISTANCE PREVENTING THE ANTI-ICE SHUTOFF VALVE TO GET A GROUND WHEN REQUIRED. NEW DIODE WAS INSTALLED AND SYSTEM FUNCTIONED CHECK NORMAL.