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SPN 729 FMI 3 — Intake air heater voltage high
SeriousEnginePower derate likely — plan to stop soon
Applies to: Paccar · Volvo
Intake air heater voltage high.
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
- Relay driver
- Wiring
- Short to voltage
- Relay stuck
FAQ
What does SPN 729 FMI 3 mean?
Intake air heater voltage high.
How serious is SPN 729 FMI 3?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 729 FMI 3?
The most common cause is: Relay driver. Other possibilities include Wiring; Short to voltage; Relay stuck.
Can I keep driving with SPN 729 FMI 3?
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.