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SPN 751 FMI 7 — Countershaft brake — not responding
SeriousTransmissionPower derate likely — plan to stop soon
Applies to: Eaton
Countershaft brake — not responding.
Don't risk it — get a diesel tech on the truck.
Look up listed providers near you and give them this SPN/FMI when you call.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Countershaft brake solenoid
- Air
- Hydraulic
First moves (roadside)
- Check air supply and brake
FAQ
What does SPN 751 FMI 7 mean?
Countershaft brake — not responding.
How serious is SPN 751 FMI 7?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 751 FMI 7?
The most common cause is: Countershaft brake solenoid. Other possibilities include Air; Hydraulic.
Can I keep driving with SPN 751 FMI 7?
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Throwing this code right now?
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.