Eaton Transmission Fault Codes
Eaton AutoShift, UltraShift PLUS, and Endurant HD fault code reference: output shaft speed signal, hydraulic pressure, shift behavior, and J1939 diagnostic context.
Eaton automated manual transmissions — AutoShift Gen 3, UltraShift PLUS, and Endurant HD — report faults through J1939 SPN/FMI codes accessible via Eaton ServiceRanger or a compatible scan tool. Verified records include output shaft speed signal quality (SPN 191 FMI 8) and hydraulic line pressure (SPN 127 FMI 1). Use the fault code lookup to search all verified records.
Transmission fault codes can originate from sensors, wiring, fluid condition, internal wear, or communication issues with the engine ECM and ABS modules. Related symptoms — delayed shifts, unexpected neutral, erratic upshift timing — may appear before a fault code becomes active, or a code may set without obvious driver-perceived symptoms depending on severity.
This site explains what fault codes mean and what areas to investigate. Repair procedures are intentionally out of scope — they depend on transmission generation, vehicle integration, and current Eaton service documentation. See the source registry for the Eaton service documents that back each verified page.
What To Know
- Output shaft speed sensor issues affect shift timing, vehicle speed reporting, and potentially ABS coordination.
- Low hydraulic pressure degrades shift quality and can trigger gear selection inhibits — check fluid level first.
- Record any companion engine or ABS codes alongside transmission codes before clearing anything.
- Do not force the truck into inhibited gear ranges when the TCM has limited them as a protective response.
FAQ
Which Eaton transmissions are covered in the verified records?
Verified pages cover fault codes from the Gen 3 AutoShift, UltraShift PLUS, and Endurant HD families. These transmissions share the same J1939 SPN/FMI reporting framework, though some diagnostic procedures and ServiceRanger workflows differ between generations.
When should a driver stop immediately with a transmission fault active?
Stop safely if the transmission cannot shift predictably, if propulsion becomes unstable on a grade, if a red stop lamp is active alongside the transmission fault, or if the truck drops unexpectedly into neutral while moving in traffic. These conditions indicate the transmission is not operating within its safe parameters.
Are Eaton transmission fault codes always mechanical failures?
No. Many Eaton AMT fault codes involve sensors, wiring, power supply, shift logic, speed signal plausibility, or communication with the engine ECM or ABS system. A fault code identifies which parameter or condition is out of range — not necessarily which physical part has failed. ServiceRanger is the appropriate tool for detailed diagnosis.