As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DEN - ON PUSHBACK FOR FLIGHT 4436 RECEIVED A APU DOOR OPEN CAUTION MESSAGE. RETURNED TO THE GATE. MAINTENANCE COMPLIED WITH A VISUAL INSPECTION OF THE APU DOOR ACTUATOR AND CLEANED THE CANNON PLUG AND THE ACTUATOR SHAFT. COMPLIED WITH DOOR INHIBIT RESET IAW AMM 49-14-19-980-803. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE. NO PARTS REPLACED.