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SPN 1209 FMI 3 — Exhaust back pressure sensor — high voltage
SeriousEnginePower derate likely — plan to stop soon
Applies to: Detroit
Exhaust back pressure sensor — high voltage.
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
- Signal short high
- Failed sensor
- Plugged line
FAQ
What does SPN 1209 FMI 3 mean?
Exhaust back pressure sensor — high voltage.
How serious is SPN 1209 FMI 3?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 1209 FMI 3?
The most common cause is: Signal short high. Other possibilities include Failed sensor; Plugged line.
Can I keep driving with SPN 1209 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.