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SPN 974 FMI 7 — ATC (automatic traction control) diff brake — not responding
SeriousAbsPower derate likely — plan to stop soon
Applies to: Bendix · Wabco
ATC (automatic traction control) diff brake — not responding.
Don't risk it — get a diesel tech on the truck.
Your SPN/FMI rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Diff brake solenoid
- Air
- Wiring
- Solenoid
First moves (roadside)
- Check ATC solenoid
- Check ATC
FAQ
What does SPN 974 FMI 7 mean?
ATC (automatic traction control) diff brake — not responding.
How serious is SPN 974 FMI 7?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 974 FMI 7?
The most common cause is: Diff brake solenoid. Other possibilities include Air; Wiring; Solenoid.
Can I keep driving with SPN 974 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.