SPN 1127 FMI 16 — Turbo Boost Pressure — High / Overboost
What it means: Measured boost is higher than commanded (overboost), or the boost reading is high.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Compare commanded vs actual boost — a large overshoot points to VGT/wastegate control.
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Listed providers nearest Sparks, NV
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- 0.0 mi away — based in Sparks, NV · (775) 355-6884
- 0.0 mi away — based in Sparks, NV · (775) 356-7200
- 0.0 mi away — based in Sparks, NV · (775) 359-0550
What SPN 1127 FMI 16 means
Measured boost is higher than commanded (overboost), or the boost reading is high. The ECM derates to protect the engine. On a variable-geometry turbo (VGT) this is frequently a sticking vane mechanism rather than a blown turbo.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Sticking VGT vanes (carbon/soot) holding too much boost
- VGT actuator fault or calibration issue
- Boost (MAP) sensor reading high or a wiring fault
- Wastegate/control fault on a wastegated turbo
First moves (roadside)
- Compare commanded vs actual boost — a large overshoot points to VGT/wastegate control.
- Check the boost sensor and wiring before assuming a mechanical turbo fault.
- Look for companion VGT actuator/position codes.
- Avoid heavy load until repaired; repeated overboost can damage the engine.
Common misdiagnoses
- Replacing the whole turbo when sticking VGT vanes just needed service/calibration.
- Condemning the actuator when the boost sensor was reading high.
- Clearing the derate without fixing the boost-control cause.
FAQ
Measured boost is higher than commanded (overboost), or the boost reading is high. The ECM derates to protect the engine. On a variable-geometry turbo (VGT) this is frequently a sticking vane mechanism rather than a blown turbo.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Sticking VGT vanes (carbon/soot) holding too much boost. Other possibilities include VGT actuator fault or calibration issue; Boost (MAP) sensor reading high or a wiring fault; Wastegate/control fault on a wastegated turbo.
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 1127 FMI 16, or share the same subsystem.
- Turbo boost pressure high (SPN 1127 FMI 0)
- Engine Protection — Power Derate Active (SPN 1569 FMI 31)
- Intake Manifold (Charge Air) Temp — High (SPN 105 FMI 0)
- 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)
- Injection control pressure low (HEUI — older engines) (SPN 164 FMI 1)
Same symptom: Low boost / low power
Other air-path codes that arrive as a truck that will not pull the hill it pulled yesterday.
- Turbo compressor inlet temp high voltage (SPN 1172 FMI 3) · Engine
- Turbo compressor inlet pressure — high voltage (SPN 1176 FMI 3) · Engine
- VGT actuator position — not responding (SPN 2795 FMI 7) · Engine
- VGT position — not responding (similar to 2795) (SPN 5571 FMI 7) · Engine
- Turbo turbine inlet temp — high voltage (SPN 5856 FMI 3) · Engine
- Turbocharger 1 Wastegate/VGT Actuator - Mechanical System Not Responding Properly (VGT vanes stuck / not tracking commanded position) (SPN 641 FMI 7) · 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.