As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CLIMB AND CRUISE, LEFT DUCT PRESSURE: 8. RIGHT DUCT PRESSURE 40. GROUNDED - YES. AIR TURNBACK - DIVERSION TIME 32 MINUTES. REMOVED AND REPLACED #1 PRESSURE RELIEF SHUTOFF VALVE REF B737-800 AMM 36-11-04. PERFORMED ENGINE BLEED AIR CROSSOVER TEST #1 AND #2 ENGINES. DUCT PRESSURES EQUAL THROUGH OUT FULL RANGE. OPS CHECK GOOD IAW AMM 36-11-00.