TSB: When completing a transaxle assembly replacement, Engine Control Module (ECM) (SAE term: Powertrain Control Module [PCM]) replacement, or ECM (PCM) reprogram, ensure the correct ECM (PCM) software is matched with the transaxle assembly hardware. Some 2017 - 2018 model year Highlander and 2017 model year Sienna vehicles require different ECM (PCM) software based on the transaxle assembly hardware installed in the vehicle. NOTICE Mismatched transaxle assembly hardware and ECM (PCM) software combinations may result in a harsh shift or shift flare. If this occurs, ECM (PCM) replacement and reprogramming will be required. If ECM (PCM) replacement/reprogramming is needed, it will not be covered under warranty. Use the information in this Service Bulletin to confirm that the correct ECM (PCM) hardware and software are used based on the transaxle assembly part number and serial number.