Fuller’s auto-shift transmissions are a boon to drivers but sometimes a headache for mechanics.
Auto-shift transmissions use what is essentially an ordinary manual transmission with an electric-motor-driven shifter assembly and an on-board electronic control unit (ECU).
Additionally, many have a second device that facilitates communication between the engine ECU and the transmission ECU.
Working on auto-shift transmissions requires extensive troubleshooting procedures before the mechanic begins changing parts, and we often see some new parts on auto-shifts that have made it to our shop after the regular mechanic gives up.
Very often, we’ll find that the mechanic replaced the ECU, the X-Y shifter and sometimes the shifter assembly in the cab, even though the troubleshooting procedures indicate there’s nothing wrong with these parts.
Often the real problem is a bad wiring harness or sensors or worn parts in the transmission.
The other common problem is that the complaint the driver is reporting doesn’t happen consistently. Perhaps it only happens once or twice per week or per month. This makes it difficult to know if the problem has been identified and repaired.