SPN 4237 FMI 16TurbochargerHigh
Turbocharger 1 Speed — Data Valid But Above Normal
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Overview
Fault Code
SPN 4237 / FMI 16
Category
Turbocharger
Fault Type
sensor
FMI Category
above normal
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: Turbocharger speed sensor on turbocharger compressor housing — reads compressor wheel speed.
Common Symptoms
- Turbocharger over-speed warning active
- Engine derate to protect turbocharger
- Possible turbocharger damage if fault ignored
- Turbo speed reading above maximum in live data
Root Causes
- VGT vanes stuck in closed position — over-spinning turbo
- Boost pressure sensor fault causing incorrect VGT command
- VGT actuator failure — vanes not opening under load
- Turbocharger speed sensor failure reading high
- Engine over-fueling causing excessive exhaust energy
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
VGT carbon buildup increases with high idle time. Turbo speed sensor failure random.
System Interactions
SPN 4237 FMI 16 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Boost pressure — engine air/fuel ratio and power output affected
EGR system — boost pressure affects EGR flow calculations
Aftertreatment — low boost can cause incomplete combustion and DPF loading
TSB Reference: Cummins TSB 4021834 — Turbocharger Speed Sensor Diagnosis and VGT Inspection
Common Diagnostic Mistakes
Replacing the sensor without verifying wiring continuity and supply voltage first.
Clearing codes without identifying and resolving the root cause — the fault will return.
Ignoring related active faults — cascading faults often share a root cause.
Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.
Condemning the ECM before exhausting all wiring and component tests.
OEM Notes
Cummins
X15: Turbo over-speed derate is a protection strategy. Address immediately — turbo failure can cause catastrophic engine damage.
Detroit
DD15: VGT carbon buildup is primary cause of turbo over-speed. DDDL VGT cleaning procedure required.
PACCAR
MX-13: Check oil supply to turbocharger — insufficient lubrication causes bearing failure and over-speed.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4237 FMI 16 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.
Authority References
Diagnostic procedures on this page are informed by OEM service literature and industry standards.
Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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