SPN 788 FMI 6 — Clutch actuator short to ground
What it means: Clutch actuator short to ground.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Disconnect motor and measure
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Louisville, KY
Closest first. Tell them SPN 788 FMI 6 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 Louisville, KY · (502) 773-1159
- 0.0 mi away — based in Louisville, KY · (502) 447-1234
- 0.0 mi away — based in Louisville, KY · (502) 648-6725
Applies to: Eaton · Volvo
What SPN 788 FMI 6 means
Clutch actuator short to ground.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Shorted motor
- Wire to ground
- Shorted coil
First moves (roadside)
- Disconnect motor and measure
- Disconnect and measure
FAQ
Clutch actuator short to ground.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Shorted motor. Other possibilities include Wire to ground; Shorted coil.
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 788 FMI 6, or share the same subsystem.
- Clutch actuator open circuit (SPN 788 FMI 5)
- Clutch actuator not responding mechanically (SPN 788 FMI 7)
- 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)
Same symptom: Won't shift
Other codes that show up as a truck that won't take a gear or drops out of one.
- Transmission output shaft speed erratic (SPN 191 FMI 2) · Drivetrain & Transmission
- Transmission output retarder position erratic (SPN 2919 FMI 2) · Drivetrain & Transmission
- Retarder not responding (SPN 2920 FMI 7) · Drivetrain & Transmission
- Gear selection failure (SPN 749 FMI 7) · Drivetrain & Transmission
- Range shift signal erratic (SPN 753 FMI 2) · Drivetrain & Transmission
- Shift finger not moving to commanded position (SPN 787 FMI 7) · Drivetrain & Transmission
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.