What are the symptoms of SPN 473 FMI 0?

Check engine light / MIL illuminated. DPF regeneration inhibited or fails to complete. Reduced engine power or derate. Excessive turbo boost readings. Poor fuel economy. Black smoke from exhaust

What causes SPN 473 FMI 0?

Exhaust backpressure sensor signal wire shorted to voltage (5V reference or battery voltage). Faulty or failed exhaust backpressure sensor providing out-of-range high voltage output. Damaged or chafed wiring harness causing short to power on signal circuit. Corroded or contaminated sensor connector causing voltage offset on signal pin. Plugged or restricted pressure sensing port/tube leading to erroneously high pressure reading. Failed ECM or ECM reference voltage circuit fault driving signal line high

How do I diagnose SPN 473 FMI 0?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 473 FMI 0 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 473 FMI 0Aftertreatment

Exhaust Pressure Sensor A Circuit High

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Overview

Fault Code

SPN 473 / FMI 0

Common Symptoms

Check engine light / MIL illuminated
DPF regeneration inhibited or fails to complete
Reduced engine power or derate
Excessive turbo boost readings
Poor fuel economy
Black smoke from exhaust

Root Causes

Exhaust backpressure sensor signal wire shorted to voltage (5V reference or battery voltage)
Faulty or failed exhaust backpressure sensor providing out-of-range high voltage output
Damaged or chafed wiring harness causing short to power on signal circuit
Corroded or contaminated sensor connector causing voltage offset on signal pin
Plugged or restricted pressure sensing port/tube leading to erroneously high pressure reading
Failed ECM or ECM reference voltage circuit fault driving signal line high

Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.

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Derate Behavior

Power Derate

Mileage / Regen Notes

An SPN 473 FMI 0 (circuit high) will typically inhibit active DPF regeneration because the ECM cannot confirm valid exhaust backpressure data needed to safely manage regen. Forced or parked regen commands may be blocked. Passive regen may continue depending on OEM calibration thresholds.

System Interactions

SPN 473 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.

DPF differential pressure monitoring — soot load calculations affected

SCR NOx conversion efficiency — DEF dosing strategy may be altered

Active regen inhibit logic — regen may be blocked or delayed

Engine protection derate — ECM may reduce power to protect components

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.

Replacing the DPF without verifying the regen system is functional — a failed regen injector will reload the new DPF.

Ignoring DEF quality — contaminated DEF causes SCR efficiency faults that look like hardware failures.

Related Faults in This Category

SPN 5246-31SCR NOx Efficiency Low SPN 4364-18DEF Dosing Below Normal SPN 3364-2DEF Quality Erratic SPN 3251-0DPF Differential Pressure High SPN 3719-16DPF Soot Load High

OEM System Resources

Cummins Fault Codes Detroit Diesel Fault Codes PACCAR Fault Codes Volvo Fault Codes Freightliner Fault Codes Mack Fault Codes

ASE Training Resources

Why ASE Certification Matters How ASE Tests Work ASE Study Tips ASE vs AI Diesel Tech Certification Paths Get Started with ASE

Diagnostic Engine v7.0

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Authority References

Diagnostic procedures on this page are informed by OEM service literature and industry standards.

EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx 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.

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