As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING ENGINES, LEFT BLEED DUCT PRESSURE INDICATES 9 PSI WITH ENGINE POWER AT IDLE, A/C PACKS IN AUTO AND ENGINE ANTI-ICE OFF. RIGHT BLEED DUCT PRESSURE INDICATES 20 PSI. GROUNDED - YES. ACCOMPLISHED VALVE HEALTH CHECK. RAN ENGINE AT IDLE NO HELP. REMOVED AND REPLACED LEFT HAND HIGH STAGE VALVE PER B737-900 AMM 36-11-06. FOUND HIGH STAGE SENSE LINE LEAKING. RE-TORQUED RAN ENGINE AT IDLE POWER PNEUMATIC NOW CHECKS NORMAL. OK FOR SERVICE.