SPN 161 FMI 2 — Input shaft speed erratic
What it means: Input shaft speed erratic.
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 Baltimore, MD
Closest first. Tell them SPN 161 FMI 2 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 Baltimore, MD · (443) 680-6789
- 0.0 mi away — based in Baltimore, MD · (410) 544-3888
- 24 hour Mobile Diesel Truck Engine Repair DEF Repairs On Site Services Road Service Laptop Diagnostic Tractors & Dump Truck☎ Call0.0 mi away — based in Baltimore, MD · (443) 591-3631
Applies to: Eaton · Volvo · I-Shift / mDRIVE share platform
What SPN 161 FMI 2 means
Input shaft speed erratic.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Speed sensor
- Tone wheel
- Wiring
- Sensor
- Wire
First moves (roadside)
- Inspect sensor
- Inspect sensor air gap
FAQ
Input shaft speed erratic.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Speed sensor. Other possibilities include Tone wheel; Wiring; Sensor; Wire.
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 161 FMI 2, or share the same subsystem.
- Main shaft speed erratic (SPN 160 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)
- Engine speed signal abnormal update rate (SPN 190 FMI 9)
- Transmission output shaft speed erratic (SPN 191 FMI 2)
- Output shaft speed abnormal (SPN 191 FMI 8)
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.