SPN 1209 FMI 3 — Exhaust back pressure sensor — high voltage
What it means: Exhaust back pressure sensor — high voltage.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Start with the most likely cause: Signal short high.
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Oklahoma City, OK
Closest first. Tell them SPN 1209 FMI 3 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 Oklahoma City, OK · (405) 551-3320
- 0.0 mi away — based in Oklahoma City, OK · (405) 682-1362
- 0.0 mi away — based in Oklahoma City, OK · (405) 632-6010
Applies to: Detroit
What SPN 1209 FMI 3 means
Exhaust back pressure sensor — high voltage.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Signal short high
- Failed sensor
- Plugged line
FAQ
Exhaust back pressure sensor — high voltage.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Signal short high. Other possibilities include Failed sensor; Plugged line.
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 1209 FMI 3, or share the same subsystem.
- Exhaust gas pressure sensor erratic (SPN 1209 FMI 2)
- Engine Protection — Power Derate Active (SPN 1569 FMI 31)
- Intake Manifold (Charge Air) Temp — High (SPN 105 FMI 0)
- Turbo Boost Pressure — High / Overboost (SPN 1127 FMI 16)
- Boost pressure high (SPN 102 FMI 0)
- Boost sensor — voltage low (SPN 102 FMI 4)
- Intake manifold temp — voltage high (SPN 105 FMI 3)
- Intake manifold temp — voltage low (SPN 105 FMI 4)
Same symptom: Charging and voltage
Other codes that trace back to voltage — one bad ground can set half a dozen of them at once.
- Turbo compressor inlet temp high voltage (SPN 1172 FMI 3) · Engine
- Turbo compressor inlet pressure — high voltage (SPN 1176 FMI 3) · Engine
- Fuel shut-off valve — voltage high (SPN 3482 FMI 3) · Engine
- Sensor supply 1 (5V) — low voltage (SPN 3509 FMI 4) · Engine
- Sensor supply 2 — low voltage (SPN 3510 FMI 4) · Engine
- Sensor supply 5 — low voltage (SPN 3513 FMI 4) · Engine
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.