As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING APU START LOW OIL PRESSURE LIGHT ILLUMINATED FOLLOWED BY THE FAULT LIGHT. EGT DID NOT RISE. GROUNDED - YES. REMOVED AND REPLACED APU LOW OIL PRESSURE SWITCH IAW B737-800 AMM 49-94-22/401. PERFORMED 3 STARTS WITH NO ISSUES. OIL PRESSURE LIGHT WENT OUT, EGT INCREASED AND NO FAULTS. APU OK FOR SERVICE. GROUND VERIFICATION CHECK C/W.