As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THERE WAS AN ODOR COMING FROM THE BLEED SYSTEM, USING THE APU BLEED AIR. SMELLED LIKE BURNING HAIR. THE ODOR WAS NOT RECOGNIZABLE WITH THE BLEED AIR OFF. REMOVED FROM SERVICE. RAN BOTH ENGINES FOR 10 MINUTES WITH BLEEDS ON. NO BURNING ODORS NOTED. NOTED NO BURNING ODORS WITH APU BLEED ON. COMPLIED WITH AMM 21-00-00-160-801, NO ODOR NOTED. RETURNED TO SERVICE.