SPN 191 FMI 8 — Output shaft speed abnormal
What it means: Output shaft speed abnormal.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Inspect sensor
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Albuquerque, NM
Closest first. Tell them SPN 191 FMI 8 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Albuquerque, NM · (505) 226-2125
- 0.0 mi away — based in Albuquerque, NM · (505) 823-9696
- 0.0 mi away — based in Albuquerque, NM · (505) 220-3541
Applies to: Eaton
What SPN 191 FMI 8 means
Output shaft speed abnormal.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Speed sensor
- Tone wheel
- Wiring
First moves (roadside)
- Inspect sensor
FAQ
Output shaft speed abnormal.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Speed sensor. Other possibilities include Tone wheel; Wiring.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside SPN 191 FMI 8, or share the same subsystem.
- Transmission output shaft speed erratic (SPN 191 FMI 2)
- Output shaft speed not updating (J1939) (SPN 191 FMI 9)
- Main shaft speed erratic (SPN 160 FMI 2)
- Input shaft speed erratic (SPN 161 FMI 2)
- Transmission output retarder speed erratic (SPN 162 FMI 2)
- Trans oil temperature very high (SPN 177 FMI 0)
- Trans oil temperature voltage high (SPN 177 FMI 3)
- Trans oil temperature voltage low (SPN 177 FMI 4)
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.