Optimum performance and reliability of heavy-duty automatic transmissions can be noticeably influenced by the type of fluid used and the frequency with which that fluid is changed. Allison Transmission has designed extensive programs including specifications and tests to verify the quality of fluids and consequently have specific fluid and filter change recommendations. Due to field studies, changes in emission requirements, vehicle design, and operating environments, Allison Transmission has realigned recommended fluid and filter change intervals. Heavy-duty Automatic Transmission change intervals have been revised to more closely match today’s operating environments. Allison has also created a new automatic transmission fluid specification, Schedule One TES 389. The new Allison specification gives OEMs and customers another approved fluid choice. Allison C4 fluids and DEXRON® fluids are no longer approved for new Commercial On-Highway products.