As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE FL 370, DUCT PRESSURE DIFFERENCE OF 24 PSI LT 24 PSI RT 48 PSI. ACFT GROUNDED. ACCOMPLISHED T/C NG-36WC-00001 ENGINE BLEED AIR HEALTH CHECK ON NR 1 ENGINE. FOUND THE PRECOOLER CONTROL VALVE NOT OPENING BY 3 PSI AND THE HIGH STAGE REGULATOR NOT WITHIN LIMITS. REPLACED PRECOOLER CONTROL VALVE REF AMM 36-12-02, OPS AND LEAK CHECKS NORMAL. REPLACED HIGH STAGE REGULATOR REF AMM 36-11-07. OPS AND LEAK CHECKS NORMAL.