As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ON TAXI OUT, AFTER BLEEDS TRANSFERRED TO APU, FLT CREW REPORTED SMOKE SMELL IN COCKPIT. PACKS SELECTED OFF AND SMOKE CLEARED. ACFT RETURNED TO GATE. MX FOUND CHECK VALVE IN LT RAM AIR DUCT BROKEN. CHECK VALVE REPLACED AND OPS CHECKED GOOD. NO SMOKE NOTED AT THIS TIME. ACFT RETURNED TO SERVICE.