As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT CREW TAXI-CHECKS, NOTICED NR 1 ENGINE DRIVEN HYD PUMP WILL NOT DEPRESSURIZE. FLT CREW ELECTED TO RETURN TO GATE. MAINTENANCE PERSONNEL CLEANED DEPRESSURIZATION SWITCH CANNON PLUG. GROUND RUN CHECK OK. AIRCRAFT RETURNED TO SERVICE. (M)