SPN 923 FMI 2 — Reverse switch erratic
What it means: Reverse switch erratic.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Check switch
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Macon, GA
Closest first. Tell them SPN 923 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 Macon, GA · (478) 538-3245
- 0.0 mi away — based in Macon, GA · (478) 216-8330
- 0.0 mi away — based in Macon, GA · (706) 536-3376
Applies to: Eaton
What SPN 923 FMI 2 means
Reverse switch erratic.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Switch
- Wiring
First moves (roadside)
- Check switch
FAQ
Reverse switch erratic.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Switch. Other possibilities include 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 923 FMI 2, or share the same subsystem.
- 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)
- Engine speed signal abnormal update rate (SPN 190 FMI 9)
- Transmission output shaft speed erratic (SPN 191 FMI 2)
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.