As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
YEG FLIGHT NR 2315: NR 1 STBY HYD PUMP HOT CAUTION LIGHT ILLUMINATED WHILE TAXING FOR TAKEOFF. ACCOMPLISHED CHECKLIST AND THE CAUTON LIGHT EXTINGUISHED SEVERAL MINUTES LATER WHILE TAXING BACK TO THE GATE. AIRCRAFT WAS FERRIED BACK TO PDX. MAINTENANCE REMOVED AND REPLACED NR 1 STANDBY POWER UNIT IAW Q400 AMM 29-11-36 PG 401-407. OPS TEST OF THE STBY PWR UNIT GOOD IAW Q400 AMM 29-11-36-710-801. NO LEAKS NOTED. AIRCRAFT RETURNED TO SERVICE.