As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU BLEED AIR SMELLS LIKE ROTTEN EGGS. ENGINE BLEED AIR SMELLS OK. RAN APU WITH BLEED AIR ON FOR 10 MIN. NO FOUL ODORS NOTICED. INSPECTED APU FOR OIL LEAKS NONE NOTED. PURGED ECS SYS AS A PRECAUTIONARY MEASURE USING APU IAW DH8-400-SL-21-012A SET UP AND PARA A. NO FURTHER DEFECTS NOTED. RETURNED TO SERVICE.